The signal transducers and activators of transcription, STAT proteins, were originally discovered in interferon (IFN)-regulated gene transcription in the early 1990’s. Since then, a number of cytokines have been recognized to activate various STAT proteins. STATs constitute a family of seven transcription factors, STAT1α/β, STAT2, STAT3α/β, STAT4, STAT5A, STAT5B and STAT6, that transduce signals from a variety of extracellular stimuli initiated by different cytokine families that aside from interferons (interferon α, β and γ) include gp130 cytokines, i.e., IL-6, IL-12, IL-23 and γC cytokines that include IL-2, IL-15 and IL-21 [1 ].