Moreover, IL-23 has a synergistic effect with IL-18 for IFN-γ production.134,135 In psoriasis, IFN-γ acts on keratinocytes, leading to the activation and production of antimicrobial peptides such as LL-37 cathelicidin and β-defensins.125 Recent studies also found that IFN-γ could induce the release of cytokines (IL-23 and IL-1) and adhesion molecules of DCs, which activate the Th17 cells.136. This evidence concerns the gene IL23A and psoriasis.