In the co-cultures (Th+B cell), IL-21 production was upregulated in both HCs and RA patients’ samples, with 33.41% ± 6.5% and 52.2% ± 8.5%, respectively, and by comparing the two groups, Th cells from RA patients showed a significantly higher IL-21 production compared to HCs. Here, IL21 is linked to rheumatoid arthritis.