IL17A and myeloid sarcoma: The role of Th17 cells in the pathogenesis of relapsing–remitting MS has been demonstrated in several studies, showing the identification of Th17 cells in the MS lesions but not in normal-appearing white matter tissues or control brain specimens (Tzartos et al., 2008) and increased levels of Th17 cell gene expression as well as IL-17 protein in MS brain lesions (Lock et al., 2002; Komiyama et al., 2006; Tao et al., 2014).