Endothelial Progenitor Cells: Relevant Players in the Vasculopathy and Lung Fibrosis Associated with the Presence of Interstitial Lung Disease in Systemic Sclerosis Patients

Endothelial progenitor cells (EPC), which are key effectors in the physiologic vascular network, have been described as relevant players in autoimmune diseases. We previously showed that EPC frequency may help to identify the presence of interstitial lung disease (ILD) in rheumatoid arthritis patients. Given that ILD constitutes the main cause of mortality in systemic sclerosis (SSc) patients, we aimed to determine the EPC contribution to the pathogenic processes of vasculopathy and lung fibrosis in SSc-ILD(+). EPC quantification was performed by flow cytometry on blood from 83 individuals: 21 SSc-ILD(+) patients and subjects from comparative groups (20 SSc-ILD(−) and 21 idiopathic pulmonary fibrosis (IPF) patients and 21 healthy controls (HC)). EPC were considered as CD34(+), CD45(low), CD309(+), and CD133(+). A significant increase in EPC frequency was found in SSc-ILD(+) patients when compared to HC (p < 0.001). SSc-ILD(+) patients exhibited a higher EPC frequency than SSc-ILD(−) patients (p = 0.012), whereas it was markedly reduced compared to IPF patients (p < 0.001). EPC frequency was higher in males (p = 0.04) and negatively correlated to SSc duration (p = 0.04) in SSc-ILD(+) patients. Our results indicate a role of EPC in the processes of vasculopathy and lung fibrosis in SSc-ILD(+). EPC frequency may be considered as a biomarker of ILD in SSc patients.