Epitopes targeted by autoantibodies in presymptomatic individuals predict early rheumatoid arthritis

To determine anticitrullinated protein antibody (ACPA) responses to novel peptides predicting the clinical outcomes of treatment-naïve early rheumatoid arthritis (RA) in the presymptomatic stage. We analysed monoclonal ACPAs derived from RA patients, including a characterised protective ACPA (clone E4), along with plasma samples collected from 520 presymptomatic individuals, of whom 244 were also sampled at diagnosis of RA, and 530 population controls in Sweden. The validation cohort (The Nordic Rheumatic Diseases Strategy Trials and Registries, NORD-STAR) consisted of 690 treatment-naïve early RA patients. Responses to citrullinated or native alpha-enolase (ENO1) or peptidylarginine deiminase 4 (PAD4) peptides were analysed by bead-based multiplex flow immunoassay. Clinical outcomes included C-reactive protein (CRP) and the 28-joint disease activity score (DAS28) with its components: tender joint count (TJC), swollen joint count (SJC), and erythrocyte sedimentation rate (ESR). Monoclonal ACPAs displayed distinct binding patterns to ENO1 and PAD4 peptides. A time-dependent increase of ACPA response to citrullinated peptides was observed in the presymptomatic stage towards onset. In the presymptomatic (0.2-5 years before onset) and early RA stage, ACPA responses to several ENO1 and PAD4 peptides were associated with less severe RA, assessed as lower levels of CRP and DAS28 and its components. In early RA, the association was more pronounced in rheumatoid factor (RF)-negative patients based on lower SJC. In presymptomatic individuals, ACPA responses widely predicted lower disease activity in early RA and were more pronounced in 5 selected peptides. Antibody responses to certain citrullinated epitopes are associated with lower disease activity in treatment-naïve early RA and appear years before symptom onset of RA.