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]. This evidence concerns the gene TNF and rheumatoid arthritis.