Furthermore, the assessment of the expression of IL-23, IL-17, and their related receptors in psoriatic skin lesions and inflamed synovium supports the concept of IL-23/IL-17 axis as a driving force of immune inflammation in psoriasis (160–164) PsA synovitis is characterized by significant infiltration of mononuclear cells, T and B cells, vascular proliferation and hyperplasia of synovial lining cells, similar to the pathological changes observed in RA (165). Here, IL17A is linked to rheumatoid arthritis.