The Complex Type 2 Endotype in Allergy and Asthma: From Laboratory to Bedside

Better management of allergic diseases needs a sharpened understanding of disease heterogeneity and mechanisms in relation to clinically significant outcomes. Phenotypes describing observable clinical and morphologic characteristics and unique responses to treatment have been developed; however, they do not relate to disease mechanisms. Recently, extended heterogeneous and disease-related metabolic, inflammatory, immunological, and remodeling pathways have been described, and reproducible patterns are defined as disease endotypes. An endotype might consist of several intricated mechanisms that cannot be clearly separated into "pure single molecular mechanism" thus being a "complex endotype." The description of an endotype may rely on biomarkers, which can be the signature of a complex underlying pathway or a key molecule associated with or directly playing a role in a particular disease endotype. The Th2 type inflammation can be defined as a complex endotype in asthma and linked to mechanisms of disease development and response to treatment and to disease outcomes such as exacerbations and remodeling. The type 2 complex endotype in allergies and asthma includes innate lymphoid cells, T helper 2 cells, tissue eosinophilia, and IgE production. Currently, emerging endotype-driven strategies in asthma, particularly the development of biologicals that target a single molecular pathway, are being focused for solving individualized clinical problems on disease outcomes. Progress is also being made for endotyping rhinitis, chronic rhinosinusitis, and atopic dermatitis.