The presence of citrullinated proteins in the inflamed synovium of arthritis-affected animals has previously been reported in different animal models [74–76], and one study reported a non-significant increase in serum ACPA levels in co-morbid mice challenged with both periodontitis (induced by oral inoculation with wild-type P. gingivalis) and arthritis, compared to corresponding animals infected with PAD-deficient P. gingivalis [58]. This evidence concerns the gene PRTN3 and periodontitis.