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 gene discussed is HOXD13; the disease is rheumatoid arthritis.