Both COVID-19 and RA exhibit an excessive immune response and cytokine imbalance, which are caused by the overactivation of T cells (especially Th1 and Th17 cells) that secrete a large number of cytokines, including TNF-α, IL-1β, IL-6, IL-8, IL-17, and GM-CSF, leading to tissue damage (Fig. 1). Here, IL17A is linked to rheumatoid arthritis.