Xing R, et al. - The levels of interleukin (IL)-21 and autoantibodies (AAbs) against IL-21 and their relationship with clinical characteristics and laboratory parameters in patients with rheumatoid arthritis (RA) are examined in this study. The levels of AAbs against IL-21 correlate with disease activity, which recommends that anti-IL-21 AAbs may play a role in the pathogenesis of RA.