In the 2000s, asthma was further subcategorised into two major endotypes: Th2 and non-Th2 asthma, based on the presence or absence of (i) CD4+ T-helper cell type 2 (Th2)-driven inflammatory responses (IL-4-, IL-5-, and IL-13-mediated), or Th17-driven responses (IL-17, IL-1β, IL-23), (ii) IgE, and (iii) increased levels of eosinophils, neutrophils, basophils, and mast cells in the airways [11]. The gene discussed is IL4; the disease is asthma.