This might suggest that these T cells travel between CSF and brain parenchyma rather than from the peripheral blood compartment to CSF, since CCR6 expression has previously been associated with the transmigration across the choroid plexus.38 The precise role of these chemokines and their receptors on the exact kinetics and timing of recruitment of T cells into the CNS of people with primary progressive multiple sclerosis remains to be elucidated. This evidence concerns the gene CCR6 and primary progressive multiple sclerosis.