Figure 1. The Notch4–Wnt–GDF15 axis in Treg cells. The UFPs and HDM (house dust mite) allergens enter the airway and are removed by the AMs, which causes a release of IL-6 that promotes the expression of Notch4 receptor on Treg cells. Notch4 signalling activates the Hippo and Wnt pathways, which can modify Treg cells leading to the activation of the Th2 and Th17 pathways. This modification produces the dysregulation of the immune tolerance. The Wnt pathway may cause the release of GDF15, promoting IL-13 release by the ILC2, which in turn contributes to the inflammatory response in allergic asthma.