IL4 and incontinentia pigmenti: In patients with AEs of IP, HO-1 is strongly and exclusively induced on M2 macrophages, which differentiate in response to IL-4, IL-10, and IL-13 and produce large amounts of TGF-β1, resulting in extracellular matrix deposition, epithelial-mesenchymal transition, fibroblast activation, and cell death, depending on M1 macrophage activation4,5,24,25.