PRTN3 and rheumatoid arthritis: In the six studies designed to investigate risk factors for AE-RA-ILD, no significant differences were observed between AE-RA-ILD and non-AE-RA-ILD groups, although rheumatoid factor (RF) and anti-cyclic citrulline polypeptide antibody (ACPA) were collected at different times and were expressed in different ways (i.e., positive or titer) [28–33].