Alexander Eggel

Flow cytometric analysis of activated basophils, known as the basophil activation test (BAT), is a tool available for the diagnosis of IgE‐mediated allergic reactions. Despite its reported clinical utility, around 10%–20% of tested subjects fall into the category of basophil non‐releasers, meaning that their basophils fail to degranulate upon IgE‐mediated stimulation in vitro. Several factors causing this non‐releaser status have been identified, but we currently lack a unified nomenclature to define such inconclusive BAT results and the practical steps to minimize such outcomes. In accordance with the STAndards for the Reporting of Diagnostic accuracy studies (STARD) statement, non‐releasers must be reported and considered in the calculation of clinical BAT performance metrics, as failure to do so significantly limits the broader implementation of BAT in routine practice. This review provides an overview of intrinsic and extrinsic factors responsible for the basophil non‐releaser phenotype in BAT. Furthermore, it proposes a standardized nomenclature for consistently reporting and integrating inconclusive BAT results in the diagnostic performance metrics and suggests diagnostic algorithms to facilitate their interpretation in clinical practice.

Food allergy is characterized by acute onset of symptoms affecting multiple organ systems following the ingestion of otherwise innocuous food antigens. The prevalence of this potentially life-threatening disease is globally increasing and poses a significant burden on society and healthcare systems. In this review, we summarize the pathophysiology of food allergy focusing on pre-clinical evidence of how oral tolerance is broken and the role of systemic and mucosal immunoglobulin E (IgE) in food allergy. Diagnosing food allergy is complex and requires a multimodal approach. Importantly, the diagnostic accuracy of currently available tests is variable, and in vivo testing runs the risk of inducing anaphylaxis in patients. We summarize established diagnostic modalities and provide an overview of novel approaches that are currently in development to improve diagnostic accuracy while minimizing discomfort and risk of anaphylaxis. Finally, we comment on available treatment modalities and provide an outlook of new therapeutic options in clinical trials or under development.

Background: Peanut allergy is among the most severe and common food allergies. The diagnosis has a significant impact on the quality of life for patients and their families. An effective management approach depends on accurate, safe, and easily implementable diagnostic methods. We previously developed a cell‐based assay using Hoxb8 mast cells (Hoxb8 MCs) aimed at improving clinical allergy diagnosis. In this study, we assessed its diagnostic performance by measuring blinded sera from a prospectively enrolled and pre‐validated peanut allergy cohort.Methods: Hoxb8 MCs were passively sensitized with sera from peanut‐allergic and peanut tolerant children and adolescents (n = 112). Degranulation of Hoxb8 MCs was quantified upon stimulation with dose‐titrated peanut extract by means of flow cytometry, using CD107a as activation marker. The results from the Hoxb8 mast cell activation test (Hoxb8 MAT) were compared to established diagnostic assays such as the skin prick test (SPT), specific IgE (sIgE) levels, and the basophil activation test (BAT). Additionally, serum samples from BAT nonresponders were assessed with the Hoxb8 MAT.Results: Hoxb8 MAT displayed a robust dose‐dependent activation to peanut extract, with a cutoff value of ≤5.2% CD107a positive cells. The diagnostic accuracy was highest at allergen concentrations ≥100 ng/mL, with an area under the receiver operating characteristic curve (AUROC) of 0.97, 93% sensitivity, and 96% specificity, outperforming traditional SPT and sIgE tests. When compared to BAT, Hoxb8 MAT exhibited comparable diagnostic efficacy. Moreover, sera from BAT nonresponders were accurately classified into allergics and nonallergics by the Hoxb8 MAT.Conclusions: The Hoxb8 MAT demonstrated a very good diagnostic precision in patients prospectively assessed for peanut allergy comparable to the fresh whole blood‐based BAT. Additionally, it demonstrated its value for accurate classification of BAT nonresponders into allergic and nonallergic individuals. Further investigations into its utility in the routine clinical setting are warranted.

Summary: The etiology of allergy is closely linked to type 2 inflammatory responses ultimately leading to the production of allergen‐specific immunoglobulin E (IgE), a key driver of many allergic conditions. At a high level, initial allergen exposure disrupts epithelial integrity, triggering local inflammation via alarmins including IL‐25, IL‐33, and TSLP, which activate type 2 innate lymphoid cells as well as other immune cells to secrete type 2 cytokines IL‐4, IL‐5 and IL‐13, promoting Th2 cell development and eosinophil recruitment. Th2 cell dependent B cell activation promotes the production of allergen‐specific IgE, which stably binds to basophils and mast cells. Rapid degranulation of these cells upon allergen re‐exposure leads to allergic symptoms. Recent advances in our understanding of the molecular and cellular mechanisms underlying allergic pathophysiology have significantly shaped the development of therapeutic intervention strategies. In this review, we highlight key therapeutic targets within the allergic cascade with a particular focus on past, current and future treatment approaches using monoclonal antibodies. Specific targeting of alarmins, type 2 cytokines and IgE has shown varying degrees of clinical benefit in different allergic indications including asthma, chronic spontaneous urticaria, atopic dermatitis, chronic rhinosinusitis with nasal polyps, food allergies and eosinophilic esophagitis. While multiple therapeutic antibodies have been approved for clinical use, scientists are still working on ways to improve on current treatment approaches. Here, we provide context to understand therapeutic targeting strategies and their limitations, discussing both knowledge gaps and promising future directions to enhancing clinical efficacy in allergic disease management.

EMPIAR, the Electron Microscopy Public Image Archive centered at EMBL-EBI, is a public resource for raw electron microscopy images related to EMDB, contains micrographs, particle sets and tilt-series.

Background: Ligelizumab is an anti‐IgE monoclonal antibody binding IgE with higher affinity than omalizumab that is under clinical investigation for several IgE‐mediated diseases. We previously showed that omalizumab removes IgE bound to FcεRI on plasmacytoid dendritic cells (pDCs) and restores their ability to produce IFN‐α and regulatory T cells (Tregs). The aim of this work is to investigate the capacity of ligelizumab to regulate functional properties of pDCs in comparison with omalizumab.Methods: pDCs were isolated from atopic donors and IgE was detached from FcεRI on pDCs with designed ankyrin repeat protein (DARPin) bi53‐79. pDCs were resensitized with IgE alone or in the presence of ligelizumab or omalizumab prior to IgE‐FcεRI crosslinking and Toll‐like receptor 9 (TLR9) stimulation. Flow cytometry, ELISA, coculture experiments and intranuclear staining were performed to determine cytokine production and Treg generation. An antigen‐specific model of resensitization and IgE‐crosslinking was also performed.Results: The levels of serum total free IgE show a non‐linear positive correlation with the frequency of IgE⁺ pDCs displaying IgE bound to FcεRI within the 43 individual donors included in the study. Ligelizumab displays stronger capacity than omalizumab to block the binding of free IgE to FcεRI on human pDCs, resulting in a greater restoration of TLR9‐L‐induced IFN‐α production. Ligelizumab also restores the ability of pDCs to generate FOXP3⁺ Tregs as previously reported for omalizumab.Conclusions: The uncovered novel molecular mechanisms of ligelizumab to regulate functional properties of pDCs from atopic donors might have important clinical implications for anti‐IgE treatments in different IgE‐mediated diseases.