Myeloid cells recruited to the CNS and the CNS resident microglia are implicated in MS pathogenesis as antigen-presenting cells, source of pro-inflammatory cytokines, and effectors of myelin destruction [11, 26, 28].The role of IL17- and IL17/IFNγ-producing CD4+ and CD8+ T cells in MS pathogenesis is debated, as conflicting data exist on the frequency of these cell subsets in the brain and cerebrospinal fluid [5, 17, 25, 29–32]. Here, IL17A is linked to myeloid sarcoma.