• IL-23/IL-23 receptor– and IL-17/IL-17 receptor–expressing cells can be found in synovial fluid, and IL-23–induced signaling can affect pannus formation, joint erosion, and osteoclastogenesis (81, 82)• IL-23 has been shown to drive enthesitis and stimulate entheseal CD3+ lymphocyte-dependent secretion of IL-17 and IL-22, inducing enthesitis and new bone formation (20)• Human entheseal tissue has been shown to contain IL-23–expressing ILC3s that may have a role in the pathogenesis of spondyloarthropathies (83). The gene discussed is IL23R; the disease is enthesitis.