HLA-DRB1 and myeloid sarcoma: In the MS-associated HLA-DR15 haplotype, the two β-chains, HLA-DRB1*1501 and -DRB5*01 are resulted in two molecules that both are functional surface heterodimers and can serve as antigen presenting molecules for myelin basic protein (MBP)-specific T cells or autoreactive T cells that are highly cytotoxic.3