AGBL2 and rheumatoid arthritis: Three generations of anti-CCP assays were developed for serological diagnosis of RA: anti-CCP1 relied on a cyclic citrullinated peptide derived from the filaggrin protein as antigen, anti-CCP2 uses synthetic cyclic citrullinated peptides, and anti-CCP3, which contains multiple citrullinated epitopes, is designed in a conformational structure to enhance epitope exposure and immunoreactivity [5,6].