TNF and psoriatic arthritis: Psoriasis (Ps) and psoriatic arthritis (PsA) are chronic, immuno-mediated inflammatory diseases characterized by abnormal expressions of keratinocytes, with actions of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, TNF-β, transforming growth factor (TGF)-β, interleukin (IL)-1, IL-6, IL-8 and IL-17 [1-3] or activation of Th2 inflammatory response, releasing TNF-α, IL-1 and IL-6, as well as proliferation and neovascularization of the synovial [4,5].