A 2014 study was the first to show that an increased number of IFN-γ-secreting TH1 and IL-17/IL-22-secreting TH17 cells were found in patients who developed TNF-α inhibitor-induced psoriasis, suggesting a potential link between TNF-α inhibitor treatment and increases in cytokines strongly associated with psoriasis, such as IL-17 and IL-22 [14]. This evidence concerns the gene IL17A and psoriasis.