The invention provides a CCP
peptide segment, an
antigen containing the CCP
peptide segment, a
reagent, a kit and an application. The CCP
peptide has a structure shown as NH2-S3-S1-X-S2-S4-COOH, X isa
citrulline-containing
epitope region, S1 and S2 are flanking regions of the
citrulline-containing
epitope region, at most one of S1 and S2 is a charged
amino acid residue, and S3 and S4 are
amino acid residue regions connected to form a loop so as to form an
amino acid residue region of the CCP peptide segment. The flanking regions of the CCP peptide segment are composed of amino acids with at most one amino acid serving as a charged amino acid, so that the intermolecular acting force can be reduced or the formation of an antigenic
epitope can be avoided, the probability is reduced that thecitrulline
antibody recognizes amino acid residues outside a key region to form an antigenic epitope and is recognized by other antibodies, thus the probability is reduced that the anti-cyclic
citrulline peptide
antibody is detected in the serum of non-RA patients, and the clinical detection specificity of the anti-cyclic citrulline peptide
antibody in the diagnosis of RA diseases is improved.