A systematic review of allergen cross-reactivity: translating basic concepts into clinical relevance

Access to the molecular culprits of allergic reactions leveraged molecular allergology as a new precision medicine approach, built on interdisciplinary, basic and clinical knowledge. Molecular allergology relies on the use of allergen molecules as in vitro tools for the diagnosis and management of allergic patients. It complements the conventional approach based on skin and in vitro allergen extract testing.Major applications of molecular allergology comprise accurate identification of the offending allergen thanks to discrimination between genuine sensitization and allergen cross-reactivity, evaluation of potential severity, patient-tailored choice of the adequate allergen immunotherapy and prediction of its expected efficacy and safety.Allergen cross-reactivity, defined as the recognition of two or more allergen molecules by antibodies or T cells of the same specificity, frequently interferes with allergen extract testing. At the mechanistic level, allergen cross-reactivity depends on the allergen, the host’s immune response and the context of their interaction. The multiplicity of allergen molecules and families adds further difficulty. Understanding allergen cross-reactivity at the immunological level and translating it into a daily tool for the management of allergic patients is further complicated by the ever-increasing number of characterized allergenic molecules, the lack of dedicated resources and the need for a personalized, patient-centered approach. Conversely, knowledge sharing paves the way for improved clinical use, innovative diagnostic tools and further interdisciplinary research. Here, we aimed at providing a comprehensive and unbiased state-of-the art systematic review on allergen cross-reactivity. For an optimal learning experience, the review was enhanced with basic, translational and clinical definitions, clinical vignettes, and an overview of online allergen databases.