HLA-DRB1 and rheumatoid arthritis: Cigarette smoking is also associated with the development of RA-ILD, as cigarette smoke inhalation induces genotoxic and inflammatory citrullination of lung antigens that extend from the conducting airway to the gas exchange zones, particularly in those patients with the shared human leukocyte antigen DRB1 (HLA-DRB1) epitope (6).