Targeting of anti-citrullinated protein/peptide antibodies in rheumatoid arthritis using peptides mimicking endogenously citrullinated fibrinogen antigens

Cátia Fernandes-Cerqueira, Elena Ossipova, Sunithi Gunasekera, Monika Hansson, Linda Mathsson, Anca I. Catrina, Yngve Sommarin, Lars Klareskog, Karin Lundberg, Johan Rönnelid, Ulf Göransson, Per-Johan Jakobsson

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). 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 binding to CCP2 utilizing the CCPlus® ELISA kit. 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 with 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. Here we demonstrate extensive autoantibody reactivity against in vivo citrullinated fibrinogen epitopes, and further show the potential use of these peptides for antagonizing ACPA.