IL17A and psoriasis: It is evident that both adaptive and innate immunity pathways play roles in the pathogenesis of psoriasis (24), these genetically susceptible patients are stimulated by external stimuli (e.g., UV or systemic drugs) production of interleukin-23 (IL-23), leading to the induction of various cytokines (including IL-17) that subsequently modify the function of keratinocytes and other skin tissue cells, either directly or through secondary mediators (23, 25).