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.