Background
Autoantibodies to citrullinated proteins (anti-CCP) can be detected in up to 80% of rheumatoid arthritis (RA) patients with very high specificity (98%). Citrulline residues, the target of the anti-CCP antibodies, are formed by post-translational modification of arginine residues, catalyzed by peptidylarginine deiminase enzymes (PAD; EC 3.5.3.15).