PRTN3 and rheumatoid arthritis: Rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPA), two serologic biomarkers for RA included in the European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) 2010 criteria (10), have been demonstrated to act as biomarkers of RA-ILD (11, 12).