TNF and rheumatoid arthritis: Other key modulators in RA are reactive oxygen species (ROS), reactive nitrogen species (RNS) and nitric oxide (NO) which are triggered by pro-inflammatory cytokines, TNF-α, IFN-γ, IL-1 and IL-2 [26–28] while anti-inflammatory cytokines, IL-4, IL-8, IL-10, IL-13 and TGF-β suppress their synthesis [29–31].