IL17A and psoriatic arthritis: IL-17 receptor is expressed in vivo in chondrocytes from different arthropathies (RA, OA, and seronegative spondyloarthropathies) [20], and IL-17 is implicated in multiple joint pathologies, such as psoriatic arthritis, ankylosing spondylitis and rheumatoid arthritis [21, 22], and drugs targeting IL-17 have been approved for treatment of psoriatic arthritis [23].