TGFB1 and rheumatoid arthritis: FLSs in inflamed synovial tissues release numerous chemokines, including CD13, IL-21, and IL-27 (99–101), which can act as chemoattractants for T cells, and the TGF-β/SMAD pathway is thought to be involved in the cross-linking between FLSs and immune cells in RA (102).