A key aspect of these pathways is the upregulation of transforming growth factor β (TGF-β), which is a signal for increased fibroblast differentiation observed in the pathogenesis of idiopathic pulmonary fibrosis (IPF) and interstitial lung disease in the course of rheumatoid arthritis (ILD-RA) (Julian and Olson, 2014; Yang et al., 2012; Zhou et al., 2013). Here, TGFB1 is linked to rheumatoid arthritis.