There are three subtypes of IFNs, i.e., type I (IFN-α and IFN-β), type II (IFN-γ), and type III (IFN-λ).117 IFNs of type I and type III can be released by several types of cells, such as epithelial cells, macrophages, and DCs, while the type II IFN is secreted by activated NK and T cells only.118,119 Recently, it has been highly recognized that IFNs serve as vital mediators in the pathogenesis of psoriasis, with type I and type II IFNs being the main mediators. This evidence concerns the gene IFNA1 and psoriasis.