CCR6 and primary progressive multiple sclerosis: In particular, we zoomed in on CD45RA− memory T cells for the expression of CSF- and/or brain residency-associated T-cell markers CD20,13 CCR5,35 CXCR3 and CCR6,35-38 as well as CCR4, a more skin-homing and T helper cell–defining marker.39,40 We showed low prevalence of B cells and an enrichment of CD4+ and CD8+ CD45RA− memory T cells in primary progressive multiple sclerosis CSF versus PBMCs (Fig. 1A and B).