CD4 and rheumatoid arthritis: The most studied bacterial strain associated with RA is related to Porphyromonas gingivalis, which is suspected of promoting autoimmunity by inducing protein citrullination, promoting HLA-DR overexpression and citrullinated peptide presentation to CD4 T cells, and by interfering with the production of cytokines and chemokines such as Jak/STAT and NF-kappaB (18, 19).