STAT3 and idiopathic pulmonary fibrosis: This was shown to be independent of gp130 expression and to be due to differential IL-6 signaling in these two fibroblast populations: in normal lung fibroblasts, IL-6 induced sustained STAT3 signaling leading to increased expression of the Cyclin Dependent Kinase Inhibitor (CDKI) p19INK4D; however, in IPF lung fibroblasts, IL-6 induced sustained SHP-2/ERK MAPK signaling leading to the decreased expression of the CDKI p27Kip1, increased Cyclin D1 activation, and enhanced proliferation (Knight et al., 2003).