The immune response to citrullinated antigens in autoimmune diseases.
Post-translational modifications of proteins occur very frequently. One of these modifications, citrullination, is the result of arginine deimination operated by an enzyme, peptidylarginine deiminase (PAD), whose activity is under strict genetic control. Serum antibodies reactive with citrullinated proteins/peptides are a very sensitive and specific marker for rheumatoid arthritis. Genes encoding for PAD enzymes have been investigated in RA: the PADI4 gene confers susceptibility to RA in Japanese patients, but not in Caucasians.