Taken together, we show the presence of citrulline-reactive gingival tissue B cells, cross-reactivity between P. gingivalis and human citrullinated peptides on a monoclonal level, and an elevated antibody response to citrullinated P.PAD in CCP2+ RA patients, supporting a scenario where the ACPA response may be partly triggered by oral infection. This evidence concerns the gene AGBL2 and rheumatoid arthritis.