Pos0442 endocitrullination of ra autoantigens is more abundant than c-terminal citrullination in the gingival crevicular fluid of anti-ccp positive at-risk individuals with periodontal disease but no synovitis

Background RA autoimmunity may be initiated at mucosal sites, including the periodontium. Anti-CCP positive at-risk individuals without synovitis (CCP+ at-risk) have an increased prevalence of periodontal disease (PD) and Porphyromonas gingivalis and an oral dysbiosis [1]. P gingivalis preferentially citrullinates C-terminal peptides by virtue of its peptidylarginine deiminase (PPAD) enzyme (2), whereas other periodontal bacteria predominantly induce endocitrullination [3]. These factors may trigger anti-citrullinated protein antibodies (ACPA), although the relative contribution of local C-terminal and endocitrullination is unclear. Objectives To determine the relative abundance of endo- and C-terminally citrullinated RA autoantigens in the gingival crevicular fluid (GCF) of CCP+ at-risk individuals with PD compared with controls. Methods CCP+ at-risk were identified from a UK cohort of anti-CCP+ individuals with musculoskeletal symptoms but no clinical synovitis. CCP+ at-risk underwent comprehensive periodontal assessment by a dentist, including GCF sampling from periodontally diseased sites. Control subjects (i.e. CCP-) with and without periodontal disease were also sampled. GCF was analysed by liquid chromatography mass spectrometry/mass spectrometry (LC-MS/MS) to identify endo- and C-terminally citrullinated peptides. The t-test was used for the statistical analysis. Results 25 CCP+ at-risk, 9 and 10 controls with and without PD respectively underwent GCF sampling. Mass spectrometry identified citrullination in 114 proteins in GCF, including 16 RA autoantigens (vimentin, myeloid cell nuclear differentiation antigen, keratin (type l/ll cytoskeletal), heterogeneous nuclear ribonucleoprotein (A2/B1, K and U), fibrinogen (alpha and beta chain), histone (H1.4, H1.5, H1x, and H4), actin (cytoplasmic 2), apolipoprotein (A-I and A-IV)). In CCP+ at-risk with PD and controls without PD there was higher total abundance of endocitrullinated RA autoantigens compared with c-terminal citrullinated autoantigens in GCF ( p <0.05, Figure 1). In CCP+ at-risk with PD 15 endocitrullinated RA autoantigens compared with only 4 C-terminally citrullinated RA autoantigens were identified (Figure 1). Fewer citrullinated RA autoantigens were identified in control subjects compared with CCP+ at-risk. More endocitrullinated compared with C-terminally citrullinated RA autoantigens were identified in controls with and without PD (Figure 1). Conclusion Several citrullinated RA autoantigens are present in the GCF of CCP+ at-risk individuals with periodontal disease but no synovitis. We identified endocitrullination as generally more abundant than C-terminal citrullination in both CCP+ at-risk and seronegative controls, suggesting PPAD may not be the primary source of citrullination. These data support the hypothesis that local citrullination of RA autoantigens at the periodontium may be an early driver of the ACPA response in RA. References [1]K. Mankia et al. . JAMA network open 2 , e195394-e195394 (2019). [2]W. T. McGraw, J. Potempa, D. Farley, J. Travis. Infection and immunity 67 , 3248-3256 (1999). [3]M. F. Konig et al. . Science translational medicine 8 , 369ra176-369ra176 (2016). Figure 1. Citrullinated RA autoantigens in gingival crevicular fluid (GCF) samples. (A ) Endocitrullinated RA autoantigens. (B ) C-terminal citrullinated RA autoantigens. * indicates p value < 0.05, t-test. PD: periodontal disease; CCP+: anti-CCP positive individuals with new musculoskeletal symptoms but no synovitis; CCP-: anti-CCP negative individuals without musculoskeletal symptoms or synovitis. Acknowledgements: NIL. Disclosure of Interests None Declared.