Introduction
Allergic diseases represent a group of conditions caused by hypersensitivity of the immune system to allergens present in the environment.1 These diseases include food allergies, asthma, atopic dermatitis (AD), allergic rhinitis (AR), conjunctivitis, and other co-morbidities and complications, such as chronic rhinosinusitis with or without nasal polyposis (CRSwNP).2-4 The 100 year old personalized allergen-specific management of allergic diseases has been a particular advantage in our specialty contributing to the early awareness of personalized approaches and precision medicine. The use of multiple omics, big data, and systems biology have demonstrated a profound complexity and dynamic variability and enabled the discovery of novel biomarkers.5
Biomarkers represent measurable indicators linking an underyling pathway to a phenotype or endotype of a disease.6-8Regrettably, current biomarkers are not precise in selecting the specific endotype that will respond to a targeted treatment. A good example is the observation that blood eosinophilia predicts therapeutic response to all currently available or future-targeted interventions in severe asthma (i.e. anti-IL-5, IL-4 /IL-13, anti-IgE-targeted treatment, CRTH2 antagonists).8,9 Precision medicine in allergic diseases demands accurate diagnoses10, which mostly rely on the combination of the clinical history and respective gold standards, which are all subject to the operator, observer and interpretation variability11,12. Some of the approaches are time-consuming, and in vivo challenges may result in severe side effects and, in rare cases, even death. Therefore, the discovery, validation and clinical applicability of molecular biomarkers become increasingly important.13
The cellular, biochemical, or molecular changes in allergic patients which are measurable in blood, sputum or nasal secretions can be considered as biomarkers.14 These biomarkers are used for disease diagnosis, selection of targeted therapy, disease monitoring and prediction of prognosis.15 Except for the well-known biomarkers (e.g, IgE, blood or sputum eosinophilia, fractional exhaled nitric oxide [FeNO]),16-18research focusing on pro-inflammatory mediators, genes, epithelial barrier and microbiomes are now emerging, which highlight more potential biomarkers for allergic diseases.19,20 Some of the biomarkers showing a strong ability in identifying disease endotypes or phenotypes may also act as therapeutic targets.21,22This article reviews the biomarkers identified to date and potential targeted therapy in allergy. In addition, it briefly reviews the biomarkers taking place in EAACI guidelines.