In summary, these results using Pg 33277 PgPAD-deficient strain and Pg 33277 wild type demonstrated that Pg PAD is engaged in elevations of citrullinated protein and ACPA without affecting the productions of host’s endogenous PADI1 and PADI4, suggesting that PgPAD is responsible for the increased pathogenic outcomes of RA by elevated productions of citrullinated protein and ACPA. Here, PADI4 is linked to rheumatoid arthritis.