TNF and systemic sclerosis: Other putative factors involved in the pathogenesis of SSc include the platelet-derived growth factors (PDGF), vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), angiotensin II, interleukin 3, interleukin 6, tumor necrosis factor-alpha (TNF-α), nerve growth factor, and fibroblast growth factor (FGF).