ACAN and rheumatoid arthritis: We synthesised citrullinated or unmodified peptide antigens from the fibrinogen, vimentin, collagen type II and aggrecan protein sequences that had been identified - either based on predicted binding capacity to RA-associated DR molecules in a molecular model positioning citrulline at P4, or through previous studies in HLA-DR4-IE-transgenic mice (Table 2) [6,15,17].