Similarly, in the case of rheumatoid arthritis (RA), HLA-DR4 molecules bearing the conserved amino acid motif (shared epitope) favor the presentation of citrullinated self-peptides leading to activation of citrulline-specific CD4+ T cells and subsequent production of anti-citrulline antibodies that foster RA but prevent natural ligands bearing arginine instead of citrulline (78). Here, CD4 is linked to rheumatoid arthritis.