PDGFA and systemic sclerosis: PDGF has been shown to cooperate with TGF-β1 in the development of organ fibrosis, and TGF-β1 can increase fibroblast sensitivity to PDGF and up-regulate PDGFR-α expression in SSc, thereby creating an autocrine PDGF-A/PDGFR-α loop [5], [6].