Bacterial citrullinated epitopes generated by Porphyromonas gingivalis infection—a missing link for ACPA production

Abstract

<jats:sec><jats:title>Objectives</jats:title><jats:p><jats:italic>Porphyromonas gingivalis</jats:italic> (<jats:italic>P.g</jats:italic>.) is discussed to be involved in triggering self-reactive immune responses. The aim of this study was to investigate the autocitrullinated prokaryotic peptidylarginine deiminase (PPAD) from <jats:italic>P.g</jats:italic>. CH2007 (RA<jats:sub>CH2007</jats:sub>-PPAD) from a rheumatoid arthritis (RA) patient and a synthetic citrullinated PPAD peptide (CPP) containing the main autocitrullination site as potential targets for antibody reactivity in RA and to analyse the possibility of citrullinating native human proteins by PPAD in the context of RA.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Recombinant RA<jats:sub>CH2007</jats:sub>-PPAD was cloned and expressed in <jats:italic>Escherichia coli</jats:italic>. Purified RA<jats:sub>CH2007</jats:sub>-PPAD and its enzymatic activity was analysed using two-dimensional electrophoresis, mass spectrometry, immunoblot and ELISA. Autoantibody response to different modified proteins and peptides was recorded and bioinformatically evaluated.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>RA<jats:sub>CH2007</jats:sub>-PPAD was capable to citrullinate major RA autoantigens, such as fibrinogen, vimentin, hnRNP-A2/B1, histone H1 and multiple peptides, which identify a common RG/RGG consensus motif. 33% of RA patients (n=30) revealed increased reactivity for α-cit-RA<jats:sub>CH2007</jats:sub>-PPAD before RA onset. 77% of RA patients (n=99) presented α-cit-specific signals to CPP amino acids 57–71 which were positively correlated to α-CCP2 antibody levels. Interestingly, 48% of the α-CPP-positives were rheumatoidfactor IgM/anti-citrullinated peptide/protein antibodies (ACPA)-negative. Anti-CPP and α-RA<jats:sub>CH2007</jats:sub>-PPAD antibody levels increase with age. Protein macroarrays that were citrullinated by RA<jats:sub>CH2007</jats:sub>-PPAD and screened with RA patient sera (n=6) and controls (n=4) uncovered 16 RA<jats:sub>CH2007</jats:sub>-PPAD citrullinated RA autoantigens and 9 autoantigens associated with lung diseases. We showed that the α-CPP response could be an important determinant in parenchymal changes in the lung at the time of RA diagnosis (n=106; p=0.018).</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>RA<jats:sub>CH2007</jats:sub>-PPAD induced internal citrullination of major RA autoantigens. Anti-RA<jats:sub>CH2007</jats:sub>-PPAD correlates with ACPA levels and interstitial lung disease autoantigen reactivity, supporting an infection-based concept for induction of ACPAs via enzymatic mimicry.</jats:p></jats:sec>

Correspondence to ‘Bacterial citrullinated epitopes generated byPorphyromonas gingivalisinfection—a missing link for ACPA production’

“…The study also provided evidence regarding how PPAD citrullinates the internal arginines of RA autoantigens. 1 Moreover, the findings of this study suggested that the failure to clear P.g. induces bacterial citrullinated epitope-specific ACPAs, which might trigger ACPA-mediated autoimmunity.…”

“…is involved in rheumatoid arthritis (RA) progression by citrullinating and producing exogenously citrullinated human and bacterial epitopes. 1 This commendable work elucidated the mechanism by which autocitrullinated prokaryotic peptidyl arginine deiminase (PPAD) mediates the inflammatory pathogenesis of RA. In particular, the authors demonstrated a correlation between anti-RA-PPAD and both anticitrullinated peptide/ protein antibody (ACPA) levels and interstitial lung disease autoantigen reactivity.…”

Infection‑provoked psoriasis: Induced or aggravated (Review)

“…The causative agent is speculated to be Porphyromonas gingivalis, a common gram-negative anaerobic periodontal pathogen, due to its unique ability to produce peptidyl arginine deiminase, the major enzyme that promotes the post-translational citrullination of peptides (51). Excessive levels of citrullinated peptides subsequently induce the production of anti-citrullinated peptide antibody (ACPA), a critical autoantibody involved in the pathogenesis of inflammatory diseases, such as RA synovitis (52). However, excessive citrullination of peptides is unlikely to increase the risk of psoriasis, as ACPA plays no role in the pathogenesis of this inflammatory skin disease (53).…”

Multifaceted Impacts of Periodontal Pathogens in Disorders of the Intestinal Barrier

“…Most RA cases are associated with the activation of bacterial citrullination and anti-cyclic citrullinated peptide antibodies. Therefore, P. gingivalis , as the only known periodontal pathogen synthesizing peptidylarginine deiminase (PPAD) that is capable of inducing the citrullination of fibrinogen and vimentin, has attracted much attention ( 128 ). However, during inflammatory arthritis, PPAD deletion in P. gingivalis mainly exacerbated P. gingivalis –induced joint inflammation.…”