Further insights regarding the mechanism by which the positively charged QKRAA, QQRAA, and KKRAA SE sequences increase the risk of RA has come from studies demonstrating that the peptide-binding P4 pocket of the HLA-DRB1 molecule, for which the SE sequence forms the sidewall, presents citrullinated antigens efficiently to T cells [6]. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.