IL21 and rheumatoid arthritis: We measured the serum IL-21 levels in RA patients (n = 120) and age-matched HC (n = 80) by ELISA and revealed that RA patients had significantly higher IL-21 levels than HC subjects (197.60 ± 32.57 vs. 59.10 ± 3.45 pg/ml, P < 0.01; Figure 1a).