Soluble programmed death molecule 1 (sPD-1) as a predictor of interstitial lung disease in rheumatoid arthritis

Previous studies have indicated that the programmed death molecule 1 (PD-1) signaling pathway may play a key role in rheumatoid arthritis (RA). However, the pathogenesis of rheumatoid arthritis-related interstitial lung disease (RA-ILD) is not clear. We examined the serum levels of soluble PD-1 in patients with RA and its relationship with RA-ILD.

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.

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 (TLC%) (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.

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.