IFNG and rheumatoid arthritis: In addition, several substances found abnormally elevated in RA synovial fluid, such as pro-inflammatory cytokines (i.e., TNF-α, IL-1β and IFN-γ) [133], Stromal cell-Derived Factor-1 (SDF-1) [134] or Immune Complexes (IC) [135] were also able to stimulate chondrocyte apoptosis, contributing to cartilage destruction in RA.