Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE‐mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE‐mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well‐defined, highly pure molecules for component‐resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the “EAACI Molecular Allergology User's Guide” (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state‐of‐the‐art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

The WHO/IUIS Allergen Nomenclature Database (http://allergen.org) provides up‐to‐date expert‐reviewed data on newly discovered allergens and their unambiguous nomenclature to allergen researchers worldwide. This review discusses the 106 allergens that were accepted by the Allergen Nomenclature Sub‐Committee between 01/2019 and 03/2021. Information about protein family membership, patient cohorts, and assays used for allergen characterization is summarized. A first allergenic fungal triosephosphate isomerase, Asp t 36, was discovered in Aspergillus terreus. Plant allergens contained 1 contact, 38 respiratory, and 16 food allergens. Can s 4 from Indian hemp was identified as the first allergenic oxygen‐evolving enhancer protein 2 and Cic a 1 from chickpeas as the first allergenic group 4 late embryogenesis abundant protein. Among the animal allergens were 19 respiratory, 28 food, and 3 venom allergens. Important discoveries include Rap v 2, an allergenic paramyosin in molluscs, and Sal s 4 and Pan h 4, allergenic fish tropomyosins. Paramyosins and tropomyosins were previously known mainly as arthropod allergens. Collagens from barramundi, Lat c 6, and salmon, Sal s 6, were the first members from the collagen superfamily added to the database. In summary, the addition of 106 new allergens to the previously listed 930 allergens reflects the continuous linear growth of the allergen database. In addition, 17 newly described allergen sources were included.

Purpose: The aim was to look at food‐allergic consumers’ preferences concerning the development of low‐allergen food.Design/methodology/approach: A questionnaire was designed to measure attitudes towards low‐allergen food. Data were collected from 20 food‐allergic consumers in Austria, Spain and The Netherlands respectively between April and May 2002 using interviewer‐assisted questionnaire methodology.Findings: The results suggested that food‐allergic consumers are interested in having low‐allergen food available, with 70‐95 per cent wanting it produced. A total of 89 per cent identified a number of benefits to themselves, including being able to resume eating the food to which they were allergic, and being able to eat all food with no worries, no symptoms and no need to check labels. Fewer disadvantages were mentioned, with 53 per cent identifying no disadvantages. Factors that would encourage or discourage purchase of low‐allergen food were also identified with price, quality (particularly taste) and safety being important. Whilst acceptance of low‐allergen food produced using genetic modification was reasonably high (55‐85 per cent), in general participants would prefer this food to be produced through conventional means.Research limitations/implications: Further research is required with a larger sample, where cross‐cultural statistical comparisons can be made. Originality/value This study provides new information about acceptability of low‐allergen food which is of use for the food industry when developing such food, benefiting both the industry and food‐allergic consumers.

Background: Birch pollen (BP) interacts with airway epithelial cells to cause allergic sensitization and allergy in predisposed individuals. However, the basic mechanisms underlying the clinical effects are poorly understood. Changes in gene expression and cytokine secretion in nasal mucosal cells upon BP exposure were determined in BP‐allergic and non‐allergic individuals.Methods: BP‐allergic (n = 11) and non‐allergic individuals (n = 12) participated in nasal provocations with saline and aqueous BP solution. Nasal scrapings and secretions were obtained at baseline and after BP provocation. Bulk RNA sequencing of the nasal scrapings was performed, and cytokines in nasal secretions were quantified.Results: After BP challenge, we identified 160 differentially expressed genes (DEGs) in the nasal scrapings of allergic individuals and 44 in non‐allergic individuals. DEGs encoding S100 proteins, keratins, small proline‐rich repeat proteins, and cytokines were predominantly identified, with proinflammatory cytokine transcripts being upregulated only in the allergic cohort. The top canonical pathways in allergic individuals included granulocyte and agranulocyte adhesion and diapedesis, wound healing, IL‐8 signaling, and IL‐17‐related pathways. Enriched pathways in allergic participants were associated with granulocyte chemotaxis, humoral cell responses, and IL‐10, IL‐4, and IL‐13 signaling and were absent in non‐allergic individuals. At baseline and after BP challenge, higher amounts of CCL17, CCL20, CCL26, IL‐7, IL‐16, and IL‐33 were detected in nasal secretions of allergic compared to non‐allergic individuals.Conclusion: Our results highlight the activation of important cellular signaling pathways specific to BP‐allergic individuals after BP exposure offering new perspectives for studying key players in BP allergy.

Background: Almond allergy is common and can manifest in two different forms. Primary almond allergy has been reported to be associated with sensitization to almond legumin Pru du 6. In birchendemic regions, there is a link between birch‐pollinosis which is likely based on a cross‐reactive Bet v 1 homologue, a yet unidentified allergen in almond. Therefore, we sought to identify and characterize a Bet v 1‐homologue in almond.Methods: The expression of a Bet v 1 homologue in almond kernels was confirmed by mass spectrometry. The recombinant protein was produced in Escherichia coli and its cross‐reactivity and allergenic potency was analyzed by IgE quantitative and competitive ELISA, immunoblotting and basophil histamine release using sera from 17 almond allergic patients.Results: The identified Bet v 1 homologue received the designation Pru du 1.0101. Pru du 1.0101 bound IgE from 82 % of almond allergic patients. Bet v 1 was able to inhibit IgE‐binding to rPru du 1 by 100%, while rPru du 1 inhibited IgE binding to rBet v 1 by 48%. Pru du 1.0101 activated basophils, though 100‐ to 1000‐fold higher concentrations were required for maximum activation in comparison to rBet v 1.Conclusion: Considering the strong inhibition capacity and higher allergenic potency of Bet v 1, the results provide compelling evidence for primary sensitization to Bet v 1 in case of birch pollen associated almond allergy. Combining Pru du 6 and Pru du 1 in diagnostic approaches may help to discriminate between primary and birch‐pollen associated almond allergy.