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 panallergen concept encompasses families of related proteins, which are involved in general vital processes and thus, widely distributed throughout nature. Plant panallergens share highly conserved sequence regions, structure, and function. They are responsible for many IgE cross-reactions even between unrelated pollen and plant food allergen sources. Although usually considered as minor allergens, sensitization to panallergens might be problematic as it bears the risk of developing multiple sensitizations. Clinical manifestations seem to be tightly connected with geographical and exposure factors. Future population- and disease-based screenings should provide new insights on panallergens and their contribution to disease manifestations. Such information requires molecule-based diagnostics and will be valuable for developing patient-tailored prophylactic and therapeutic approaches. In this article, we focus on profilins, non-specific lipid transfer proteins, polcalcins, and Bet v 1-related proteins and discuss possible consequences of panallergen sensitization for the allergic patient. Based on their pattern of IgE cross-reactivity, which is reflected by their distribution in the plant kingdom, we propose a novel classification of panallergens into ubiquitously spread "real panallergens" (e.g. profilins) and widespread "eurallergens" (e.g. polcalcins). "Stenallergens" display more limited distribution and cross-reactivity patterns, and "monallergens" are restricted to a single allergen source.

T cells play an important role in the pathogenesis of allergic diseases. However, the proteins considered as potential immunogens of allergenic T-cell responses have traditionally been limited to those that induce IgE responses. Timothy grass (TG) pollen is a well-studied inhaled allergen for which major IgE-reactive allergens have also been shown to trigger T helper 2 (Th2) responses. Here we examined whether other TG pollen proteins are recognized by Th2 responses independently of IgE reactivity. A TG pollen extract was analyzed by 2D gel electrophoresis and IgE/IgG immunoblots using pooled sera from allergic donors. Mass spectrometry of selected protein spots in combination with de novo sequencing of the whole TG pollen transcriptome identified 93 previously undescribed proteins for further study, 64 of which were not targeted by IgE. Predicted MHC binding peptides from the previoulsy undescribed TG proteins were screened for T-cell reactivity in peripheral blood mononuclear cells from allergic donors. Strong IL-5 production was detected in response to peptides from several of the previously undescribed proteins, most of which were not targeted by IgE. Responses against the dominant undescribed epitopes were associated with the memory T-cell subset and could even be detected directly ex vivo after Th2 cell enrichment. These findings demonstrate that a combined unbiased transcriptomic, proteomic, and immunomic approach identifies a greatly broadened repertoire of protein antigens targeted by T cells involved in allergy pathogenesis. The discovery of proteins that induce Th2 cells but are not IgE reactive may allow the development of safer immunotherapeutic strategies.

Climate change and air pollution, including ozone is known to affect plants and might also influence the ragweed pollen, known to carry strong allergens. We compared the transcriptome of ragweed pollen produced under ambient and elevated ozone by 454-sequencing. An enzyme-linked immunosorbent assay (ELISA) was carried out for the major ragweed allergen Amb a 1. Pollen surface was examined by scanning electron microscopy and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), and phenolics were analysed by high-performance liquid chromatography. Elevated ozone had no influence on the pollen size, shape, surface structure or amount of phenolics. ATR-FTIR indicated increased pectin-like material in the exine. Transcriptomic analyses showed changes in expressed-sequence tags (ESTs), including allergens. However, ELISA indicated no significantly increased amounts of Amb a 1 under elevated ozone concentrations. The data highlight a direct influence of ozone on the exine components and transcript level of allergens. As the total protein amount of Amb a 1 was not altered, a direct correlation to an increased risk to human health could not be derived. Additional, the 454-sequencing contributes to the identification of stress-related transcripts in mature pollen that could be grouped into distinct gene ontology terms.