Moreover, specific RA characteristics, such as serum positivity for anti-citrullinated protein/peptide antibodies (ACPA) (16, 17), and/or the rheumatoid factor (RF) (13, 18), the presence of the RA-associated human leukocyte antigen HLA-DR4, and the presence of other extra-articular manifestations, in particular subcutaneous nodules, were found to be significant predictors for ILD development [(6, 19, 20); Table 1]. Here, PRTN3 is linked to rheumatoid arthritis.