Background/Purpose: Recently, periodontal disease (PD) has been associated with the risk and progression of RA.  Patients with RA complicated by PD have been shown to have higher anti-citrullinated protein antibody (ACPA) levels, which have also become predictive markers of the disease and its severity.  Previous studies have demonstrated that RA can be induced in mice following oral infection with P. gingivalis (P. ging), a major cause of PD.  However, these studies never demonstrated antibody or T-cell responses to citrullinated antigens.  Therefore, it was the purpose of this study to determine whether infection with P. ging can induce RA and if these responses induce antibodies and/or T-cell responses to select citrullinated antigens in DBA/1J mice.

Methods: DBA/1J mice were subjected to sulpha-methoxazole in their water for 10 days and then gavaged with P. ging 3 times over a 1 week period. Control mice were subjected to antibiotics in the absence of P. ging and injected with mouse type II collagen collagen (Col).  Also, mice were immunized with citrullinated Col (Cit-Col) in parallel as previously published.  Animals were evaluated weekly for inflammation of the joints for 6 weeks and sacrificed followed by serum and spleen collection.  The CD4⁺ T cells were then isolated and proliferated against Col, Cit-Col or P. ging outer membrane antigen (PGMA).  Serum was tested for the presence of antibody to PGMA and ACPA, the latter using a second generation anti-CCP assay.

Results: At week 6, mice gavaged with P. ging had a significant increase in inflammation as assessed by paw thickness (2.883 mm) and scoring (3.25) compared to the respective controls (2.543 mm) and (1.6); P≤0.01 between groups.   Similar results were demonstrated for the Cit-Col groups, 2.868 mm and 3.25 (P≤0.001vs. controls).  There was nearly a 2-fold increase in serum ACPA in the P. ging infected mice (11.2 U/ml) compared to no infection (6.89 U/ml) (p=0.002).  The Cit-Col injected animals showed an ACPA response of 10.8 U/ml which was significantly different from controls (P=0.02). Antibody to PGMA was significantly higher in both the P. ging infected animals (4.101 µg/ml) and the Cit-Col (2.714 µg/ml) injected mice compared to controls (1.201 µg/ml) (P≤0.01 for both groups).  CD4⁺ T-cells from P. ging infected mice proliferated to both Cit-Col (5.34 stimulation index (SI)) and to PGMA (16.68 SI) compared to controls which had SI’s of (0.160) and (0.704) respectively P≤0.001.  T-cells from mice immunized with Cit-Col proliferated to Cit-Col at (3.950 SI) and to PGMA at (4.829 SI).  This proliferative response was not observed with exposure of T-cells from both P.ging or Cit-Col injected mice to P .intermedia (an alternative cause of PD) membrane antigen.    

Conclusion: These data show that following infection with P. ging, DBA/1J mice develop an inflammatory arthritis that is characterized by the expression of ACPA.  Furthermore, T-cells from mice immunized with Cit-Col or infected with P. ging showed increased proliferation to both Cit-Col and PGMA.  This suggests a cross reactivity between the PGMA and the citrullinated antigen.  These studies begin to provide some insight into mechanisms linking P. ging with RA pathogenesis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/t-cell-cross-reactivity-with-citrullinated-antigen-and-p-gingivalis-membrane-antigen-following-infection-with-p-gingavalis-andor-injection-of-citrullinated-mouse-type-ii-collagen-in-dba1j-mice/