HOXD13 and rheumatoid arthritis: Levels of serum sPD-1 were significantly higher in the RA-ILD group than in the RA-non-ILD group (185.1 ± 109.0 pg/ml vs 119.1 ± 77.5 pg/ml, P = 0.003, Fig. 1A) and healthy controls (185.1 ± 109.0 pg/ml vs 52.1 ± 21.7 pg/ml, P < 0.0001, Fig. 1A).