According to the classical Th1/Th2 model by which naïve Th cells differentiate into either Th1 or Th2 cells producing the defining cytokines interferon gamma (IFNγ) and interleukin (IL)-4, respectively, psoriasis was classified as a Th1 disease with a marked type 1 cytokine profile [13]. This evidence concerns the gene IFNG and psoriasis.