TNFSF11 and rheumatoid arthritis: IL-17 is a key contributor to arthritic inflammation in RA and PsA [44,52,73], and can exacerbate tissue inflammation by upregulating proinflammatory cytokines such as TNF and IL-1β, and contribute to osteoclastogenesis and bone resorption by promoting the expression of RANKL [74,75].