Repertoire expansion of antibodies against citrullinated protein antigens (ACPA) is associated with RA susceptibility [15], articular damage [16], and the presence and extent of radiographic RA-ILD [7], suggesting that citrullination of lung proteins and/or pathogenic ACPA may contribute to the pathogenesis of RA-ILD, perhaps via interfering with the normal functioning of targeted proteins or via pathologic antigen/antibody interactions. Here, PRTN3 is linked to rheumatoid arthritis.