Background Antibodies against citrulline, a post-translational protein modification (PTM), define a large RA patient subset characterised by severe disease course. Antibodies against another PTM residue, homocitrulline, have recently been described in the sera of early RA patients and in individuals with arthralgia where they predicted RA development. It is thus possible that antibodies against further PTMP are present in the sera of RA patients.
Objectives To investigate the antibody reactivity against a panel of PTM vimentin peptides in patients with early inflammatory arthritis.
Methods Microtitre plates were coated with vimentin peptides identical in length and composition except at one amino acid that was changed to introduce a citrullinated, carbamylated or acetylated residue. Vimentin was chosen as the backbone owing to its expression in RA synovium, the known role of citrullinated vimentin peptides in increasing MHC affinity and T cell activation and the high specificity and sensitivity for a diagnosis of RA associated with anti-citrullinated vimentin antibodies. Sera of 268 treatment naïve patients with early inflammatory arthritis and symptoms ≤3 months duration were tested. Outcomes were defined at 18 month follow-up. Anti-CCP antibody levels were determined with a commercial anti-CCP2 assay (ELiA™). Sera of patients that tested positive for antibodies against all modifications were preincubated with each of the modified peptides in competition experiments and antibody reactivities determined to investigate binding specificity.
Results The proportion of patients with positive antibody tests was significantly higher in the anti-CCP RA group (n=48) compared to anti-CCP negative RA (n=53), persistent non-RA (n=55) and resolving arthritis (n=112) groups for reactivities against citrullinated (p<0.0001), carbamylated (p<0.0001) and acetylated (p<0.0001) peptides (Figure 1). No antibody reactivity was observed against the unmodified vimentin peptide in any group. Competition experiments revealed negligible cross-reactivity between antibody populations.
Conclusions We show for the first time that antibodies against acetylated vimentin are present in the sera of patients with anti-CCP positive early RA and confirm and extend previous observations regarding anti-citrullinated and anti-carbamylated antibodies. Anti-CCP positive RA patients displayed a distinct antibody profile indicating a specific rather than generic response to inflammatory arthritis. Negligible cross-reactivity between antibody subsets denoted that antibodies are directed to specific antigens. Lysine acetylation is a possible mechanism through which microbiome can affect their host. Interestingly, recent sequencing of the intestinal microbiome revealed a high prevalence of Prevotella copri in patients with early RA suggesting a pathogenic role. The presence of antibodies against acetylated lysine proteins in these patients may provide a link between microbiome, self-antigen acetylation and autoimmunity in early RA.
Disclosure of Interest None declared