Furthermore, by analyzing mRNA expression, Conrad et al. demonstrated that the expression of the type I IFNs IFNA2 and IFNB1 was significantly greater in skin lesions caused by TNF-α inhibitor-induced psoriasis than in those caused by chronic plaque psoriasis, while no significant difference in the expression levels of other cytokines, such as TNF, IL23A, IL17A, IL17F, and IL17C, were detected between skin lesions caused by TNF-α inhibitor-induced psoriasis and those caused by classical psoriasis [47]. This evidence concerns the gene IL17F and psoriasis.