IL4 and asthma: IL-4 and IL-13 play crucial roles in T2high asthma because of their capacity to drive Th2 cell differentiation and IgE production and because these cytokines can directly influence lung structural cells, especially fibroblasts, smooth muscle cells, and epithelial cells, and, as such, contribute to features of remodeling (collagen deposition, smooth muscle cell thickening, and epithelial shedding).