Consistent with their potential involvement in the pathogenesis of MS, the relative frequency of IL-17A+ CD4+ memory T cells in the CSF was consistently and significantly increased in MS but not OND (Fig. 1D), as well as their absolute number (Fig. 1G) as previously described (Brucklacher-Waldert et al., 2009, Durelli et al., 2009), although even in persons with MS they constituted only a small percentage of the total cells in the blood and CSF. Here, IL17A is linked to myeloid sarcoma.