CD4 and psoriasis: Psoriasis lesions are marked by infiltration of immune cells in the dermis, such as macrophages, dendritic cells and neutrophils (Sabat et al., 2019), and macrophages and dendritic cells secrete IL-23, which in turn induces IL-17 production by CD4+T cells (Hansel et al., 2011), thus suggesting that IL-23 is the main upstream regulator leading to the development of psoriasis lesions.