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Bacterial citrullinated epitopes generated by Porphyromonas gingivalis infection—a missing link for ACPA production
  1. Madeleine Jenning1,
  2. Bianka Marklein1,
  3. Jimmy Ytterberg2,3,
  4. Roman A Zubarev4,
  5. Vijay Joshua5,
  6. Dirkjan van Schaardenburg6,
  7. Lotte van de Stadt6,
  8. Anca Irinel Catrina7,
  9. Ute Nonhoff8,
  10. Thomas Häupl1,
  11. Zoltán Konthur8,9,
  12. Gerd R Burmester1,
  13. Karl Skriner1
  1. 1 Department of Rheumatology and Clinical Immunology, Charité University Medicine Berlin, Corporate Member of Free University Berlin, Humboldt University Berlin and Berlin Institute of Health, Berlin, Germany
  2. 2 Swedish Orphan Biovitrum AB, Stockholm, Sweden
  3. 3 Department of Medical Biochemistry and Biophysics, Division of Physiological Chemistry I, Stockholm, Sweden
  4. 4 Medical Biochemistry and Biophysics, Chemistry I Division, Karolinska Institute, Stockholm, Sweden
  5. 5 Rheumatology Unit, Department of Medicine, Karolinska University Hospital and Institutet, Stockholm, Sweden
  6. 6 Jan van Breemen Research Institute | Reade, Amsterdam, The Netherlands
  7. 7 Rheumatology Unit, Stockholm, Sweden
  8. 8 Engine GmbH, Hennigsdorf, Germany
  9. 9 Bundesanstalt für Materialforschung und –prüfung (BAM), Berlin, Germany
  1. Correspondence to Dr Karl Skriner, Department of Rheumatology and Clinical Immunology, Charité University Medicine Berlin, corporate member of Free University Berlin, Humboldt University Berlin and Berlin Institute of Health, Berlin 10117, Germany; karl.skriner{at}


Objectives Porphyromonas gingivalis (P.g.) 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 P.g. CH2007 (RACH2007-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.

Methods Recombinant RACH2007-PPAD was cloned and expressed in Escherichia coli. Purified RACH2007-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.

Results RACH2007-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-RACH2007-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-RACH2007-PPAD antibody levels increase with age. Protein macroarrays that were citrullinated by RACH2007-PPAD and screened with RA patient sera (n=6) and controls (n=4) uncovered 16 RACH2007-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).

Conclusions RACH2007-PPAD induced internal citrullination of major RA autoantigens. Anti-RACH2007-PPAD correlates with ACPA levels and interstitial lung disease autoantigen reactivity, supporting an infection-based concept for induction of ACPAs via enzymatic mimicry.

  • infections
  • early rheumatoid arthritis
  • autoantibodies
  • autoimmunity

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  • Handling editor Josef S Smolen

  • Correction notice This article has been corrected since it published Online First. The legend for figure 5 has been corrected and a further affiliation for Zoltán Konthur has been added and the supplementary citation has been corrected in the results section.

  • Contributors MJ wrote the first draft of the manuscript. All authors involved in drafting the manuscript and approved the final version.

  • Funding The work was supported by grants from the project ArthroMark (grant number: 01EC1401A).

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Patient consent for publication Obtained.

  • Ethics approval The study was approved by the ethics committee of the Charité University Hospital Berlin, Germany and by the institutional ethics committees of the participating clinics.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.

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