TGFB1 and systemic sclerosis: SSc fibroblasts also express platelet-derived growth factor (PDGF) and its receptors; PDGF is a chemoattractant for fibroblasts, forcing them to produce collagen and to secrete TGF-β1, IL-6, and monocyte chemoattractant protein 1 (MCP-1), thus strengthening the development of fibrosis [38].