POS0395 ANTI-ACETYLATED PROTEIN ANTIBODIES IN RHEUMATOID ARTHRITIS (RA): CLUES FOR THE STARTING POINT OF AUTOANTIBODY RESPONSES IN RA

Background: Rheumatoid arthritis (RA) is characterized by autoantibodies such as rheumatoid factor (RF) and anti-modified protein (AMPAs) like anti-citrullinated antibodies (ACPA) anti-carbamylated (anti-CarP). Recently, another AMPA: anti-acetylated (AAPA) have been found in RA patients [1]. The prevalence of AAPA their isotypes yet to be determined. Since isotype profiles reflect the breadth an immune response, with without can help understand relevance this autoantibody response RA. Objectives: To describe Methods: In 650 fulfilling 1987 criteria 555 non-RA from Leiden Early Arthritis Cohort, baseline serum samples were screened ELISA for IgG, IgM IgA acetylated- control peptide that was based upon CCP-2 backbone. cutoff positivity on 80 controls (mean + 2SD). A sample considered positive if it above 0.1 optical density higher acetylated than peptide. Results: IgG 36% versus 6.7% (figure 1a). Within patients, mostly present ACPA-(CCP-2) group (64% ACPA-positive, compared 5% ACPA-negative). Levels healthy 1b), however, surprisingly, no difference levels IgM. When AAPA- compared, more often two or then RA, thus displayed considerably overlap (table 1). Intriguingly, most prevalent patients. Table 1. Anti-acetylated antibody (=310) n (% ) Non-RA (n=106) IgG+IgM-IgA- 115 (37.1) 28 (5.1) IgG-IgM+IgA- 52 (16.8) 48 (8.7) IgG-IgM-IgA+ 14 (4.5) 13 (2.3) IgG+IgM+IgA- 24 (7.7) 3 (0.5) IgG+IgM-IgA+ 37 (11.9) 4 (0.7) IgG-IgM+IgA+ 9 (2.9) 8 (1.4) IgG+IgM+IgA+ 59 (19.0) 2 (0.4) AAPA: antibodies, RA: Conclusion: are detected one third mainly ACPA-positive subgroup. predominance suggests persons develop development These results also suggest individuals, responses occur, but do not mature past IgM-stage, while AAPA-response does might form a “starting point” other AMPA leading concurrent several disease. References: [1]Juarez, M., et al., Identification novel antiacetylated vimentin early inflammatory arthritis. Ann Rheum Dis, 2016. 75 (6): p. 1099-107. Disclosure Interests: None declared