Furthermore, IL-21 induced B cells to produce higher levels of IgG and IgM in RA patients (IgG: 297.20 ± 24.77 vs. 353.70 ± 29.30 ng/ml, P < 0.05; IgM: 12.43 ± 4.39 vs. 20.47 ± 9.73 ng/ml, P > 0.05; Figure 5d) compared to HC (IgG: 221.60 ± 18.19 vs. 258.50 ± 24.51 ng/ml, P < 0.05; IgM: 3.29 ± 0.18 vs. 3.03 ± 0.19 ng/ml, P > 0.05; Figure 5d), although there were no marked differences in the secretion of IgM. Here, IL21 is linked to rheumatoid arthritis.