However, only the citrullinated peptides trigger an effective response of antigen-specific CD4+ T cells in RA [12] except for HLA-DRB1*14:02 [13], in which both native and citrullinated peptides showed similar binding affinities, likely due to polymorphisms that alter the P4 pocket. Here, HLA-DRB1 is linked to rheumatoid arthritis.