Rheumatoid Arthritis and Infections   

Hussein Mahajna, ... Howard Amital, in Infection and Autoimmunity (Second Edition), 2015

Gingival infection caused by is another that is associated with RA. It is postulated that this microbe causes a citrullination process in human proteins that leads to a cascade causing autoimmunity.26Periodontitis, in which P. gingivalis is a major pathogenic bacterium, has been linked to RA in epidemiological studies, and they share similar genomic and environmental associations. It is also the only bacterium identified that expresses endogenous citrullinated proteins and its own bacterial PAD enzyme.24 Antibody titers to P. gingivalis are significantly increased in patients with RA and significantly correlated with anti-CCP antibody isotypes that are specific to RA.27 Additional studies indicate that the major synovial targets of the RA-specific anti-CCP autoantibodies are deamidated forms of the α- and β-chains of fibrin. Other studies confirmed that bacterial PAD produced by P. gingivalis has the capacity of deamidating arginine in fibrin found in the periodontal lesion.28Citrullination of HLA binding peptides causes a 100-fold increase in peptide–major histocompatibility complex affinity and leads to the activation CD4(+)T cells in HLA DRB1 0401 transgenic mice.28

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