CD8+ T cells are also present in psoriasis, produce the same range of cytokines as CD4+ cells, and reside predominantly within the epidermis [5, 10].Over the last decade, it has been shown that the main source of IL-17 in psoriasis is not T cells, but rather innate cells like neutrophils and mast cells [11–14]. Here, IL17A is linked to psoriasis.