PRTN3 and rheumatoid arthritis: Studies have suggested that this association may be based on the ability of P. gingivalis to express peptidyl deiminase (PAD), an enzyme responsible for citrullination of arginine residues post-translation, which can expose individuals to citrullinated antigens and easily lead to ACPA in the appropriate immunogenetic background, possibly contributing to the pathogenesis of RA synovitis (Hitchon et al., 2010).