Objective
To determine the relationship between serum soluble programmed death molecule-1 (sPD-1) levels and the development of interstitial lung disease (ILD) in patients with rheumatoid arthritis (RA).
Methods
Blood samples were obtained from 87 patients with RA (58 with ILD and 29 without ILD) and 45 healthy controls. Serum sPD-1 was measured by enzyme-linked immunosorbent assay. The pulmonary interstitial disease score was completed by a pulmonary physician and a radiologist through chest high-resolution computed tomography. Patients with RA-ILD were tested for lung function [e.g., forced vital capacity (FVC%), diffusing capacity of lungs for carbon monoxide (DLCO%)]. Associations between ILD and various markers, including sPD-1 and confounding factors, were investigated by logistic regression analysis. Diagnostic values of sPD-1 for the presence of ILD were investigated using receiver operating characteristic curve analysis.
Results
Serum sPD-1 levels were higher in RA patients with ILD than in RA patients without ILD and healthy controls (185.1 ± 109.0 pg/ml vs. 119.1 ± 77.5 pg/ml vs. 52.1 ± 21.7 pg/ml, P < 0.05). Serum sPD-1 levels were positively correlated with RF titer (P = 0.02, r = 0.249), anti-cyclic citrullinated peptide antibody status (P = 0.02, r = 0.243), and serum IgG levels (P < 0.001, r = 0.368), negatively associated with FVC% (P = 0.02, r = − 0.344), forced expiratory volume (FEV1%) (P = 0.01, r = − 0.354), total lung capacity % (P = 0.046, r = − 0.302), and was independently associated with the presence of ILD in RA patients by multivariate logistic regression analysis. The sensitivity and specificity of sPD-1 levels for the detection of ILD in RA patients were 58.6% and 75.9%, respectively. The area under the curve was 0.689.
Conclusion
Serum sPD-1 levels were increased in RA patients with ILD. Increased sPD-1 may be a valuable biomarker to predict the presence of ILD in patients with RA.