In psoriasis (PsO) and psoriatic arthritis (PsA), the skin microenvironment is enriched with pro-inflammatory cytokines such as IL-23, IL-12, IL-17, TNF-α, and IFN-α, largely produced by dendritic cells and other innate immune cells in response to antimicrobial peptides (AMPs). The gene discussed is IL17A; the disease is psoriasis.