Several HLA class I associations with MS have also been identified, such as the strongest known protective alleles HLA-A*02:01 and HLA-B*38:01 (25) mentioned above, although untangling HLA associations with disease is notoriously difficult due to linkage disequilibrium and also other factors such as killer-immunoglobulin receptor (KIR) type, which can have a significant effect on immune activation in natural killer (NK) cell subsets (56). This evidence concerns the gene HLA-A and myeloid sarcoma.