In addition, studies have shown that in the lungs of smokers, PAD2 and PAD4 expressed by neutrophils can citrullinate the cathelicidin human cationic antimicrobial protein-18 (chcap-18) that can be potentially externalized by NETosis to promote RA (146, 148, 150, 151). This evidence concerns the gene PADI2 and rheumatoid arthritis.