HOXD13 and rheumatoid arthritis: 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).