We found that psoriasis samples exhibited differential expression of genes associated with Th17 inflammation, including the Th17 recruiting chemokine CCL20; NOS2 and ARG1/2, which stimulate Th17 differentiation; the Th17 cytokines IL-17A and IL-17F; NFKBIZ, a mediator of Th17 signalling in keratinocytes; the Th17-induced antimicrobial peptides DEFB4A, DEFB103B, S100A9 and S100A8; the Th17-induced cytokines IL-19, IL-36A, IL-36G, IL-36RN, and CXCL8; and the Th17-dependent pro-angiogenic factor CXCR2 (Fig. 1a). Here, IL17F is linked to psoriasis.