Similarly, the serum levels of IL-17, IL-21, and IL-23, cytokines associated with Th17 cell responses, are significantly elevated in RA patients compared with those in osteoarthritis patients, and the frequencies of detectable IL-6, IL-17, and IL-21 are greater in the active RA group than in the inactive RA group [147]. This evidence concerns the gene IL21 and osteoarthritis.