Representative mass cytometry images of (a, a’, b, b’) control white matter, (c, c’, d, d’) normal-appearing white matter (block no. CR4A), (e, e’, f, f’) (p)reactive lesion (block no. CR4A), (g, g’, h, h’) active demyelinating lesion (block no. CR4A) and (i, i’, j, j’) mixed active-inactive demyelinating lesion (block no. CL3A). For each region of interest, we show the same area simultaneously labeled with markers of antigen presentation (human leukocyte antigen, HLA) to detect microglia and/or macrophages, TMEM119 to detect microglia, lysosomes (CD68) to detect phagocytic cells and DNA (Ir-intercalator). (a, a’– i, i’) Overlay of TMEM119 (red), HLA (green) and Ir-intercalator (blue) identifies (dotted arrows in a’ and c’) TMEM119+HLA- resting microglia with thin elongated processes and (arrows head in a’,c’, e’, i’ and e’’) TMEM119+HLA+ activated microglia or (solid arrows in a’, c’, e’, g’, i’ and g’’) TMEM119-HLA+ activated macrophages. (b, b’–j, j’’) Overlay of CD68 (red), HLA (green) and Ir-intercalator (blue) identifies HLA+CD68+ phagocytic microglia/macrophages. PPWM, periplaque white matter; BV, blood vessel.