IL17A and psoriasis: Precisely, TNFα and IL‐17A have been considered as major players in the pathogenesis of psoriasis, since Chiricozzi et al. identified that costimulation of keratinocytes with TNFα and IL‐17A leads to synergistic upregulation of hundreds of genes, including a group of genes with the highest level of expression in psoriatic skin, such as IL‐8, IL‐17C, IL‐19, CCL20 and DEFB4.65