FLG and rheumatoid arthritis: In order to compare ACPA reactivity to the pro-filaggrin peptide originally employed for determination of ACPA in a streptavidin capture ELISA, we screened 20 RA sera and 20 sera from healthy donors for reactivity to biotinylated cyclic and linear versions (LCPa, CCPa) and non-citrullinated controls (LCPg, CCPg).