title: Targeting of anti-citrullinated protein/peptide antibodies in rheumatoid arthritis using peptides mimicking endogenously citrullinated fibrinogen antigens.
abstract: BACKGROUND
  We have previously identified endogenously citrullinated peptides derived from fibrinogen in rheumatoid arthritis (RA) synovial tissues. In this study, we have investigated the auto-antigenicity of four of those citrullinated peptides, and explored their feasibility to target anti-citrullinated protein/peptide antibodies (ACPA).
  
  
  METHODS
  The autoantigenic potential of the fibrinogen peptides was investigated by screening 927 serum samples from the Epidemiological Investigation of RA (EIRA) cohort on a peptide microarray based on the ImmunoCAP ISAC® system. In order to assay for ACPA blocking, two independent pools of purified ACPA were incubated with the respective targeting peptide prior to binding to cyclic citrullinated peptide (CCP)2 using the CCPlus® ELISA kit.
  
  
  RESULTS
  Two peptides derived from the fibrinogen α chain, Arg573Cit (563-583) and Arg591Cit (580-600), referred to as Cit573 and Cit591, and two peptides from the fibrinogen β chain, Arg72Cit (62-81) and Arg74Cit (62-81) (Cit72 and Cit74), displayed 65%, 15%, 35%, and 53% of immune reactivity among CCP2-positive RA sera, respectively. In CCP2-negative RA sera, a positive reactivity was detected in 5% (Cit573), 6% (Cit591), 8% (Cit72), and 4% (Cit74). In the competition assay, Cit573 and Cit591 peptides reduced ACPA binding to CCP2 by a maximum of 84% and 63% respectively. An additive effect was observed when these peptides were combined. In contrast, Cit74 and Cit72 were less effective. Cyclization of the peptide structure containing Cit573 significantly increased the blocking efficiency.
  
  
  CONCLUSIONS
  Here we demonstrate extensive autoantibody reactivity against in vivo citrullinated fibrinogen epitopes, and further show the potential use of these peptides for antagonizing ACPA.
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. catia.cerqueira@ki.se.
authors.forename: Cátia
authors.initials: C
authors.lastname: Fernandes-Cerqueira
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. elena.ossipova@ki.se.
authors.forename: Elena
authors.initials: E
authors.lastname: Ossipova
authors.affiliation: Division of Pharmacognosy, Department of Medicinal Chemistry, Biomedical Centre, Uppsala University, Husargatan 3, 751 23, Uppsala, Sweden. sunithi.gunasekera@fkog.uu.se.
authors.forename: Sunithi
authors.initials: S
authors.lastname: Gunasekera
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. monika.hansson@ki.se.
authors.forename: Monika
authors.initials: M
authors.lastname: Hansson
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Dag Hammarskjölds v 20, 751 85, Uppsala, Sweden. linda.mathsson@igp.uu.se.
authors.forename: Linda
authors.initials: L
authors.lastname: Mathsson
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. anca.catrina@ki.se.
authors.forename: Anca I
authors.initials: AI
authors.lastname: Catrina
authors.affiliation: Euro-Diagnostica AB, Lundavägen 151, 202 11, Malmö, Sweden. yngve.sommarin@eurodiagnostica.com.
authors.forename: Yngve
authors.initials: Y
authors.lastname: Sommarin
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. lars.klareskog@ki.se.
authors.forename: Lars
authors.initials: L
authors.lastname: Klareskog
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. karin.lundberg@ki.se.
authors.forename: Karin
authors.initials: K
authors.lastname: Lundberg
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Dag Hammarskjölds v 20, 751 85, Uppsala, Sweden. johan.ronnelid@igp.uu.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Rönnelid
authors.affiliation: Division of Pharmacognosy, Department of Medicinal Chemistry, Biomedical Centre, Uppsala University, Husargatan 3, 751 23, Uppsala, Sweden. ulf.goransson@fkog.uu.se.
authors.forename: Ulf
authors.initials: U
authors.lastname: Göransson
authors.affiliation: Rheumatology Unit, Department Medicine, Karolinska University Hospital, Solna, Rheumatology Clinic D2:01, 171 76, Stockholm, Sweden. per-johan.jakobsson@ki.se.
authors.forename: Per-Johan
authors.initials: PJ
authors.lastname: Jakobsson
mesh_terms: D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D002956:Citrulline / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D005340:Fibrinogen / Q000276:immunology*; D006801:Humans; D010455:Peptides / Q000276:immunology; D010456:Peptides, Cyclic / Q000276:immunology*; D040081:Protein Array Analysis
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D010455:Peptides; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D002956:Citrulline; D005340:Fibrinogen