The pathogenesis of rheumatoid arthritis (RA) is not fully understood. However, it is thought to arise from a mixture of genetic factors including human leukocyte antigen-antigen D-related (HLA-DR) and environmental factors, particularly infection and smoking.1 Three infectious agents, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Epstein-Barr virus (EBV), are strongly associated with the triggering of autoimmunity in RA.2
Anticitrullinated protein antibodies (ACPAs) play a critical role in the pathogenesis of RA, and their production is indicative of a break in immune tolerance.2 Detection of ACPAs and of rheumatoid factor is part of the diagnostic criteria for RA.3 ACPAs have been found to precede the clinical onset of RA, to predict the development of the disease, to be present in a majority of patients with RA, and to be linked to a more severe course of the pathology.2,4,5
Citrullination, a posttranslational modification of proteins catalyzed by peptidyl arginine deiminase (PAD), may result in neoantigens activating T cells, thus helping B cells drive the ACPA response in RA.2 ACPAs recognize citrullinated autoantigens associated with an HLA-DRB1 shared epitope (HLA-DRB1SE), including fibrinogen α and β chains, enolase-1, vimentin, collagen II, histone 4, P gingivalis enolase, and EBV (EBNA 1 and 2).2
Although the current paradigm of RA pathogenesis points to these posttranslational antigen modifications as the main player driving ACPA+ autoimmunity, questions about the role of autoantibodies remain.6
Rheumatology Advisor interviewed Maximilian F. Konig, MD, from Harvard Medical School in Boston, Massachusetts, about a recent study he coauthored with Felipe Andrade, MD, PhD, during his time at Johns Hopkins University in Baltimore, Maryland.6 The study contributed to the understanding of the role of antinative protein antibodies in RA pathogenesis. “We looked at the RA33 antibody in RA and found that patients targeted this autoantigen in 3 very different ways. Some targeted RA33 only as a citrullinated protein (not recognizing the native antigen), some targeted it only as a native protein, and another small subset had truly cross-reactive antibodies that were able to target both the native and citrullinated protein similarly.”
The researchers found that antibodies against native RA33 were much more common in patients with mild and recently diagnosed RA. “This suggests that the anti-native RA33 response may precede the ACPA response in some patients with RA,” Dr Konig noted. He explained that there might be an evolution of the antibody response in some patients with RA, with the native antigen being targeted first, followed by a more mature ACPA response.
Infections and Generation of ACPA in RA
Periodontal disease (PD) is common in adults and caused by organisms such as P gingivalis and A actinomycetemcomitans; such infections may result in the synthesis of ACPA and a loss of tolerance.2
P gingivalis synthesizes 2 enzymes, PAD and arginine gingipains, which can be secreted from the bacterial outer membrane.7,8 PAD from P gingivalis can citrullinate human peptides, including fibrinogen and enolase-2 RA antigens, and was found to enable the progression of destructive arthritis in animals.9,10 In a recent large Swiss epidemiologic study, arginine gingipain type B antibodies were found to be higher in patients with RA compared with in controls, to be higher in ACPA+ vs ACPA− patients with RA, and to be more strongly associated with RA than smoking. The authors concluded, “Our study suggests that the previously reported link between periodontitis and RA could be accounted for by P. gingivalis infection, and we conclude that P. gingivalis is a credible candidate for triggering and/or driving autoimmunity and autoimmune disease in a subset of RA patients.”11
P gingivalis can also trigger neutrophil extracellular trap formation, which provides a source of native autoantigens including enolase, histones, and vimentin.2,12 Neutrophil extracellular trap neutrophils are found in the joints and nodules of patients with RA.13
A actinomycetemcomitans is associated with aggressive PD,14 is found in 47% of ACPA+ patients with RA,2 and causes citrullination of a large number of proteins. Citrullination occurs through the production of leukotoxin A and neutrophil PAD activation. In addition, only in patients with RA who have been exposed to A actinomycetemcomitans is HLA-DRB1SE associated with ACPA.6
EBV belongs to the herpes family and infects the majority of adults2; however, EBV DNA is increased up to 10 times in peripheral blood mononuclear cells (lymphocytes and monocytes) of patients compared with healthy EBV carriers.15
Antibodies against citrullinated EBNA 1 and 2 have been found in patients with RA.2 The presence of EBNA 2 has been found to precede symptom onset in RA, predict disease development, and be associated with HLA-DRB1SE.16 Transfer of ectopic lymphoid structures containing RA synovia into immunodeficient mice results in the production of antibodies directed against citrullinated EBNA 1 and EBNA 2.17
Evidence indicates that EBV may trigger an immune response that initiates a loss of tolerance through cross-reactivity and epitope-spreading.2
Moving Toward Antigen-Specific Immunotherapy
Current RA therapies treat symptoms or slow disease progression, but are associated with many adverse effects, including immune suppression. Antigen-specific immunotherapy targets subsets of B or T cells, leaving systemic host defense uncompromised.18
An encouraging example of antigen-specific immunotherapy comes from a 2015 open-label phase1 trial that tested the efficacy of a combination of 4 citrullinated peptide antigens (aggrecan, vimentin, collagen type II, and fibrinogen), designated Rheumavax.19 Ranjeny Thomas, MD, chair of rheumatology at the University of Queensland, Australia, spoke with Rheumatology Advisor about the study. “We evaluated the safety and effect of a high, and a low, dose of autologous dendritic cells modified with an inhibitor and exposed to 4 citrullinated antigens in 18 ACPA+ RA patients who carried the HLA-DR shared epitope. Sixteen controls did not receive dendritic cells,” she said. Rheumavax was well-tolerated, and at 1 month, effector T-cells were reduced (P <.05), and an improved ratio of regulatory to effector T cells was found.
“We also observed a decrease in cytokines, chemokines and C-reactive protein, suggesting an anti-inflammatory effect,” Dr Thomas added. Assessment of antigen-specific responses was limited in this study. However, the researchers stated, “Tetanus toxoid-specific T cell proliferative responses were not suppressed after Rheumavax, suggesting that Rheumavax was not broadly immunosuppressive.”
Also, a phase 1b clinical trial was recently started to evaluate the safety and immunological response of DEN-181 in ACPA+ patients with RA. This antigen-specific nanoparticle-based immunotherapy will use single-ascending and multidose protocols in a double-blind placebo-controlled manner.20
Continued research is needed to guide a clearer understanding of the role infectious agents, ACPAs, and antinative protein antibodies play in RA autoimmunity with the goal of finding more targeted immunotherapies that cure or prevention RA.
- McInnes IB, Schett G. The pathogenesis of rheumatoid arthritis. N Engl J Med. 2011;365(23):2205-2219.
- Sakkas LI, Daoussis D, Liossis SN, et al. The infectious basis of ACPA-positive rheumatoid arthritis. Front Microbiol. 2017;8:1853.
- Aletaha D, Neogi T, Silman AJ, et al. 2010 rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis Rheum. 2010;62(9):2569-2581.
- van Gaalen FA, Linn-Rasker SP, van Venrooij WJ, et al. Autoantibodies to cyclic citrullinated peptides predict progression to rheumatoid arthritis in patients with undifferentiated arthritis: a prospective cohort study. Arthritis Rheum. 2004;50(3):709-715.
- van der Helm-van Mil AH, Verpoort KN, Breedveld FC, et al. Antibodies to citrullinated proteins and differences in clinical progression of rheumatoid arthritis. Arthritis Res Ther. 2005;7(5):R949-R958.
- Konig MF, Giles JT, Nigrovic PA, et al. Antibodies to native and citrullinated RA33 (hnRNP A2/B1) challenge citrullination as the inciting principle underlying loss of tolerance in rheumatoid arthritis. Ann Rheum Dis. 2016;75(11):2022-2028.
- Potempa J, Pike R, Travis J. The multiple forms of trypsin-like activity present in various strains of Porphyromonas gingivalis are due to the presence of either Arg-gingipain or Lys-gingipain. Infect Immun. 1995;63(4):1176-1182.
- McGraw WT, Potempa J, Farley D, et al. Purification, characterization, and sequence analysis of a potential virulence factor from Porphyromonas gingivalis, peptidylarginine deiminase. Infect Immun. 1999 Jul;67(7):3248-3256.
- Wegner N, Wait R, Sroka A, et al. Peptidylarginine deiminase from Porphyromonas gingivalis citrullinates human fibrinogen and α-enolase: implications for autoimmunity in rheumatoid arthritis. Arthritis Rheum. 2010;62(9):2662-2672.
- Maresz KJ, Hellvard A, Sroka A, et al. Porphyromonas gingivalis facilitates the development and progression of destructive arthritis through its unique bacterial peptidylarginine deiminase (PAD). PLoS Pathog. 2013;9(9):e1003627.
- Kharlamova N, Jiang X, Sherina N, et al. Antibodies to porphyromonas gingivalis indicate interaction between oral infection, smoking, and risk genes in rheumatoid arthritis etiology. Arthritis Rheumatol. 2016;68(3):604-613.
- Delbosc S, Alsac JM, Journe C, et al. Porphyromonas gingivalis participates in pathogenesis of human abdominal aortic aneurysm by neutrophil activation. Proof of concept in rats. PLoS One. 2011;6(4):e18679.
- Khandpur R, Carmona-Rivera C, Vivekanandan-Giri A, et al. NETs are a source of citrullinated autoantigens and stimulate inflammatory responses in rheumatoid arthritis. Sci Transl Med. 2013;5(178):178ra40.
- Haubek D, Johansson A. Pathogenicity of the highly leukotoxic JP2 clone of Aggregatibacter actinomycetemcomitans and its geographic dissemination and role in aggressive periodontitis [published online August 14, 2017]. J Oral Microbiol. doi: 10.3402/jom.v6.23980
- Balandraud N, Meynard JB, Auger I, et al. Epstein-Barr virus load in the peripheral blood of patients with rheumatoid arthritis: accurate quantification using real-time polymerase chain reaction. Arthritis Rheum. 2003;48(5):1223-1228.
- Johansson L, Pratesi F, Brink M, et al. Antibodies directed against endogenous and exogenous citrullinated antigens pre-date the onset of rheumatoid arthritis [published online June 3, 2016]. Arthritis Res Ther. doi:10.1186/s13075-016-1031-0
- Croia C, Serafini B, Bombardieri M, et al. Epstein-Barr virus persistence and infection of autoreactive plasma cells in synovial lymphoid structures in rheumatoid arthritis. Ann Rheum Dis. 2013;72(9):1559-1568.
- Pozsgay J, Szekanecz Z, Sármay G. Antigen-specific immunotherapies in rheumatic diseases. Nat Rev Rheumatol. 2017;13(9):525-537.
- Benham H, Nel HJ, Law SC, et al. Citrullinated peptide dendritic cell immunotherapy in HLA risk genotype-positive rheumatoid arthritis patients. Sci Transl Med. 2015;7(290):290ra87.
- Human trials begin for potential world-first rheumatoid arthritis treatment [press release]. Brisbane, Queensland: Uniquest. Published November 14, 2017. Accessed November 27, 2017.