TGFB1 and systemic sclerosis: These results suggest that PDGF-AA up-regulated PDGFR-α over-expression on the surface of SSc fibroblasts to initiate signal transduction via PDGF-A/PDGFR-α and to promote fibroblast trandifferentiation to myofibroblasts in skin lesions of SSc patients, and these effects were enhanced by TGF-β1.