IL17A and myeloid sarcoma: Although CCR6 is known to be expressed by a number of pathogenic and regulatory CD4+ Th subsets (Comerford et al., 2010), the high expression of CCR6 on CSF CD4+ T cells in MS has been previously attributed to IL-17-secreting Th17 cells without determination of the actual frequency of these cells (Reboldi et al., 2009).