Endotypes of Atopic Dermatitis: Correspondence to Classical Subtypes

Since atopic dermatitis (AD) is a heterogeneous condition, subtyping of AD is a crucial issue. The classical subtypes of AD are represented by extrinsic and intrinsic subtypes, European American and Asian subtypes, and adult and pediatric subtypes. While subtyping of AD was historically conducted based on the phenotype, recent findings on the mechanisms of AD have revealed importance of the endotype, which can characterize individual patients more accurately. Considering the current development of AD therapies, AD endotyping is prerequisite for personalized therapeutic choice. Endotypes of AD can be stratified from different viewpoints, including cytokine expression patterns, allergen properties, epidermal barrier conditions, ceramide variation, involvement of innate immunity, and serum biomarkers. Among them, the cytokine-based endotype seems to be the most useful one and is categorized into type 2 cytokine (IL-4, IL-13 and IL-31)-high, type 1 cytokine (interferon-g)-high, and/or type 3 cytokine (IL-22 and IL-17)-high, or mixed subtypes. The recently biomarker-proposed endotyping aims at individualized treatment options, although the daily clinical use of endotypes is a future issue. To better understand the endotypes for clinicians, attempts to adjust each of the classical subtypes to the endotypes are required. This review will discuss the correspondence of the classical subtypes to the various endotypes that have recently been proposed.