This study on the role of IL-6 and IL-21 during Th17 differentiation and the development of experimental arthritis revealed synergistic effects of IL-6 and IL-21 signaling pathways in driving Th17 differentiation in vitro, and indicated that the IL-6/IL-21 combination blocking strategy may be a highly effective way of treating patients with early rheumatoid arthritis. Here, IL21 is linked to rheumatoid arthritis.