CD4 and rheumatoid arthritis: Activated memory CD4 T cells migrating between the blood and synovium express cytokines (TNF-α, IFN-γ, IL-17, GM-CSF) and activation markers (receptor activator of nuclear factor κB ligand, osteoclast differentiation factor), contributing to tissue damage in RA (Wu et al. 2020; Emery et al. 2014; McInnes and Schett 2007; Jiang et al. 2020).