IL17F and psoriasis: The aims of this study are to assess changes in cytokine levels (TNF-α, IL-12/23, IL-17A, IL-17F) after 12 weeks of biologic treatment in psoriasis to test if there is any correlation between their serum level and PASI (Psoriasis Area Severity Index) and DLQI (Dermatology Life Quality Index) scores before or after treatment and to check the influence of clinical and lifestyle factors on these levels.