PF4 and systemic sclerosis: Furthermore, CXCL4 stimulates B cells to secrete autoantibodies [82], induces the proliferation of SSc-derived T cells [82], and enhances the secretion of platelet-derived growth factor (PDGF)-BB by monocytes, a growth factor that is increased in dcSSc patients and has been shown to enhance fibronectin and collagen deposition by fibroblasts [88].