Variability in the HLA-DRB genes influences antigen binding, and the 1501 allele is thought to increase MS risk by increasing binding to and presentation of aromatic residues present in the myelin basic protein to the Tcell receptor (Ota et al., 1990), leading to increased numbers of MBP-reactive Tcells (Oksenberg et al., 1993). Here, HLA-DRB1 is linked to myeloid sarcoma.