title: Heightened immune response to autocitrullinated Porphyromonas gingivalis peptidylarginine deiminase: a potential mechanism for breaching immunologic tolerance in rheumatoid arthritis.
abstract: BACKGROUND
  Rheumatoid arthritis (RA) is characterised by autoimmunity to citrullinated proteins, and there is increasing epidemiologic evidence linking Porphyromonas gingivalis to RA. P gingivalis is apparently unique among periodontal pathogens in possessing a citrullinating enzyme, peptidylarginine deiminase (PPAD) with the potential to generate antigens driving the autoimmune response.
  
  
  OBJECTIVE
  To examine the immune response to PPAD in patients with RA, individuals with periodontitis (PD) and controls (without arthritis), confirm PPAD autocitrullination and identify the modified arginine residues.
  
  
  METHODS
  PPAD and an inactivated mutant (C351A) were cloned and expressed and autocitrullination of both examined by immunoblotting and mass spectrometry. ELISAs using PPAD, C351A and another P gingivalis protein arginine gingipain (RgpB) were developed and antibody reactivities examined in patients with RA (n=80), individuals with PD (n=44) and controls (n=82).
  
  
  RESULTS
  Recombinant PPAD was a potent citrullinating enzyme. Antibodies to PPAD, but not to Rgp, were elevated in the RA sera (median 122 U/ml) compared with controls (median 70 U/ml; p<0.05) and PD (median 60 U/ml; p<0.01). Specificity of the anti-peptidyl citrullinated PPAD response was confirmed by the reaction of RA sera with multiple epitopes tested with synthetic citrullinated peptides spanning the PPAD molecule. The elevated antibody response to PPAD was abolished in RA sera if the C351A mutant was used on ELISA.
  
  
  CONCLUSIONS
  The peptidyl citrulline-specific immune response to PPAD supports the hypothesis that, as a bacterial protein, it might break tolerance in RA, and could be a target for therapy.
authors: Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, , London, UK.
authors: Anne-Marie
authors: AM
authors: Quirke
authors: Elena Birgitta
authors: EB
authors: Lugli
authors: Natalia
authors: N
authors: Wegner
authors: Bart C
authors: BC
authors: Hamilton
authors: Peter
authors: P
authors: Charles
authors: Muslima
authors: M
authors: Chowdhury
authors: A Jimmy
authors: AJ
authors: Ytterberg
authors: Roman A
authors: RA
authors: Zubarev
authors: Jan
authors: J
authors: Potempa
authors: Shauna
authors: S
authors: Culshaw
authors: Yonghua
authors: Y
authors: Guo
authors: Benjamin A
authors: BA
authors: Fisher
authors: Geoffrey
authors: G
authors: Thiele
authors: Ted R
authors: TR
authors: Mikuls
authors: Patrick Jw
authors: PJ
authors: Venables
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D001323:Autoantibodies / Q000276:immunology; D016866:Bacteroidaceae Infections / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D002956:Citrulline / Q000378:metabolism; D005260:Female; D006801:Humans; D006867:Hydrolases / Q000235:genetics* / Q000276:immunology*; D007108:Immune Tolerance / Q000235:genetics* / Q000276:immunology; D008297:Male; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010456:Peptides, Cyclic / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010518:Periodontitis / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D016966:Porphyromonas gingivalis / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D000076342:Protein-Arginine Deiminases
chemical_list: D001323:Autoantibodies; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D002956:Citrulline; D006867:Hydrolases; D000076342:Protein-Arginine Deiminases
keywords: Ant-CCP; Autoimmunity; Rheumatoid Arthritis