Stability of the immunoglobulin M anticitrullinated protein antibody response. Sera taken from 18 patients at baseline (BL) and at 1, 2 and 5 years of follow-up were analyzed by ELISA for reactivity against cyclic citrullinated peptide 2 (CCP2), fibrinogen (Fib)-α and Fib-β. (A) through (C) Graphs displaying the immunoglobulin M (IgM) reactivity to the indicated peptides over time. The absorbance of citrulline (cit) reactivity minus absorbance of the arginine (arg) reactivity is shown. (D) Table showing the number of positive patients at baseline (BL) as well as the conversion toward negative or positive during one of the follow-up (FU) time points analyzed.