IL17A and myeloid sarcoma: Multiple lines of evidence suggest a role for Th17 in MS pathogenesis, including an elevated frequency of Th17 cells in the CSF as compared to the blood, increased Th17 frequencies in both blood and CSF during relapses (Brucklacher-Waldert et al., 2009, Durelli et al., 2009), and the detection of IL-17A+ T cells in brain parenchyma from MS post-mortem tissue (Tzartos et al., 2008).