IL17F and arthritic joint disease: Joint inflammation–Human/patient data: IL-17F is expressed in the synovial tissue from RA patients and contributes to human chronic joint inflammation in vitro and in vivo (62, 70, 71)–Animal models: IL-17F is increased in CIA (78), while playing only marginal roles on CIA and arthritis in Il1rn−/− mice (72, 74).