CCN2 and systemic sclerosis: While we observed decreased level of several soluble profibrotic growth factor receptors such as TGFBR3 and PDGFR-alpha in SSc serum, a previous study has indicated an increased level of N-terminal connective tissue growth factor (CTGF) in SSc plasma [41], indicating that profibrotic growth factor levels might be increased in SSc serum while the soluble receptor levels of profibrotic growth factors are low.