18 month timepoints after correction for multiple testing. A similar pattern was observed for IgA ACPA antibody levels, although IgG ACPA levels did not vary significantly comparing baseline with 6, and 6 with 18 month timepoints. Antibody levels were not influenced by exposure to therapy. Patients seropositive for anti-CCP2 at baseline demonstrated less labile antibody levels, with the exception of sustained increases in IgG ACarPA reactivity compared with seronegative individuals. Abstract

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... 0104figure 1. demonstrates bidirectional changes in anti-PTM antibody reactivity at the patient level. Abstract THU0104 - Figure 1 . Fold change in anti-PTM autoantibody levels between baseline and 18 months in patients with newly-presenting rheumatoid arthritis (n=130) Conclusions: Median AAPA and, to a lesser extent, ACPA levels fell over time, regardless of therapy. This was most marked for the IgA isotype. Differential isotype effects may represent maturation of the autoantibody repertoire from mucosal IgA antibodies involved in the breach of tolerance. Lability of AAPA levels may reflect the relative reversibility of acetylation of a lysine amino acid residue by comparison with citrullination and carbamylation modifications. By contrast, and as observed previously 3 , IgG ACarPA levels increased over time, perhaps reflecting the tendency of the human proteome to accrue carbamylation modifications due to ageing, and metabolic or inflammatory stress.