Both IL-17A and IL-17F have been implicated in the pathogenesis of inflammatory joint diseases such as osteoarthritis and rheumatoid arthritis, where increased concentrations have been detected in synovial fluid, meniscal tissue, and articular cartilage, with IL-17A levels in osteoarthritic synovia typically ranging from 5 to 10 pg/mL [11,13,15]. Here, IL17A is linked to osteoarthritis.