The present invention relates to an antigenically effective peptide comprising, from the amino to the carboxylic terminal, the amino acid sequence: G P P W W P P I C D P P Q P S K T Q G Q S X 1 G Q S X 2 G X 3 G X 4 G X 5 G X 6 G X 7 G K G K S X 8 D K Q X 9 K P G G P W X 10 P E P (SEQ ID No. 1), wherein the amino acids X 1 -X 10 are selected independently from an arginine residue or a citrulline residue and at least one of X 1 -X 10 is a citrulline residue, or a functional fragment thereof and uses thereof.