TGFB1 and rheumatoid arthritis: Notably, TGFβ1, a regulatory cytokine that affects proliferation, differentiation, and survival of several types of cells, promotes the redirection of naÏve T cells from a Th2 to Th9 cell differentiation pathway [43] and was abundantly seen in most actively proliferating synovial intimal cells from patients with RA [44].