TNF and rheumatoid arthritis: Additionally, TGF-β1 has a synergistic effect with TNFα on the expression of IL-1β in RA synovial fibroblasts [49] and induces the proliferation of synovial fibroblasts through platelet-derived growth factor (PDGF)-AA and cMyc induction, resulting in a massive synovial hypertrophy in the affected joints [50].