In this study, we examined the physical characteristics of a citrullinated pro-filaggrin epitope using RA sera in a streptavidin capture enzyme-linked immunosorbent assay (ELISA) using the original pro-filaggrin sequence CCP1 (HQCHQEST-Cit-GRSRGRCGRSGS) with special emphasis on peptide structure, peptide length and peptide presentation. This evidence concerns the gene FLG and rheumatoid arthritis.