BackgroundThe presence of anti-citrullinated protein antibodies (ACPA) is a powerful predictive factor for the development and progression of rheumatoid arthritis (RA). The ACPA response has been shown to consist of various isotypes, but the consequences of differences in isotype distribution have not been extensively investigated.ObjectiveTo investigate the relationship between ACPA isotypes, disease progression and radiological outcome.MethodsACPA isotypes were determined in sera of anti-cyclic citrullinated peptide 2-positive patients by enzyme-linked immunosorbent assay (ELISA). To investigate whether the ACPA response continues to evolve during disease development, the ACPA isotype profile during progression of undifferentiated arthritis (UA) to RA was studied. The association of disease progression with ACPA isotype use was assessed using long-term radiographic follow-up data from patients with RA in two independent cohorts.ResultsThe ACPA isotype distribution did not expand during disease progression from UA to RA, but was relatively stable over time. In both RA cohorts, the baseline ACPA isotype profile was a significant predictor of disease severity, with more isotypes indicating a higher risk of radiographic damage (odds ratio for every additional isotype: 1.4 (95% CI 1.1 to 1.9) p<0.001). ACPA isotypes supplied additional prognostic information to ACPA status alone, even after correction for other predictive factors.ConclusionsThe magnitude of the ACPA isotype profile at baseline reflects the risk of future radiographic damage. These results indicate that the presence and the constitution of the ACPA response are relevant to the disease course of RA.