Endothelial Progenitor Cells as a Potential Biomarker in Interstitial Lung Disease Associated with Rheumatoid Arthritis.

Interstitial lung disease (ILD) increases morbidity and mortality in patients with rheumatoid arthritis (RA). Although the pathogenesis of ILD associated with RA (RA-ILD+) remains poorly defined, vascular tissue is crucial in lung physiology. In this context, endothelial progenitor cells (EPC) are involved in endothelial tissue repair. However, little is known about their implication in RA-ILD+. Accordingly, we aimed to investigate the potential role of EPC related to endothelial damage in RA-ILD+. EPC quantification in peripheral blood from 80 individuals (20 RA-ILD+ patients, 25 RA-ILD- patients, 21 idiopathic pulmonary fibrosis (IPF) patients, and 14 healthy controls) was performed by flow cytometry. EPC were considered as CD34+, CD45low, CD309+ and CD133+. A significant increase in EPC frequency in RA-ILD+ patients, as well as in RA-ILD- and IPF patients, was found when compared with controls (p < 0.001, p = 0.02 and p < 0.001, respectively). RA-ILD+ patients exhibited a higher EPC frequency than the RA-ILD- ones (p = 0.003), but lower than IPF patients (p < 0.001). Our results suggest that EPC increase may represent a reparative compensatory mechanism in patients with RA-ILD+. The degree of EPC frequency may help to identify the presence of ILD in RA patients and to discriminate RA-ILD+ from IPF.