HLA-DRB1 and rheumatoid arthritis: Thus, research conducted over several decades has demonstrated a pivotal contribution to disease pathogenesis of HLA-DRB1 alleles encoding the “Shared Epitope” (SE) (HLA-DRB1 SE), a conserved amino acid sequence located at positions 70–74 in the β-chain of the class II HLA-DR molecule [9, 10], specifically among RA patients positive for disease-specific anti-citrullinated protein antibodies (ACPAs) [11–13].