In healthy donors and psoriasis patients, we found a similar frequency of IL-17+ Th17 cells (1.2 ± 0.3% versus 1.6 ± 0.4%) whereas the percentage of IL-17+/IFN-γ+ Th17 cells is increased in patients (0.44 ± 0.1; P < 0.05; Supplementary Figure 1(b)). Here, IL17A is linked to psoriasis.