PRTN3 and rheumatoid arthritis: Among the non-classical autoantibodies putatively correlated with ILD in patients with RA, anti-citrullinated alpha-enolase peptide 1 (anti-CEP-1) have been identified as a subset of ACPA associated with erosive RA and ILD (82), particularly at high titers (106), and have been proposed for early detection of RA-ILD in at risk non-smoking patients (82).