Details, distribution and characteristics of various cell types. (A) Centrum semiovale oligodendrocytes, some with a clear perinuclear halo, in a control sample (H&E). (B) Oligodendrocytes with nuclear reactivity for Olig2 in the control centrum semiovale. (C) Centrum semiovale the 4H patient with rarefaction of myelin, increased microglia, astrocytes and decreased numbers of oligodendrocytes (H&E). (D) Centrum semiovale in the 4H patient with markedly decreased numbers of Olig2-positive oligodendrocytes; only 4 to 5 oligodendrocytes are seen in this high power field. (E, F) Corpus callosum oligodendrocytes in a control sample (H&E, E; Olig2, F). (G) Corpus callosum in 4H patient with rarefaction, increased microglia and astrocytes and decreased numbers of oligodendroglia (H&E). (H) Corpus callosum in 4H patient oligodendrocytes with nuclear reactivity for olig2 showing decreased numbers of labeled oligodendrocytes. (I) Control sample cerebral cortex; there are 3 to 6 perineuronal oligodendrocytes per neuron in this plane of section (H&E). (J) Control sample cerebral cortex showing perineural and perivascular oligodendrocytes immunoreactive to Olig2. (K) Cerebral cortex in 4H patient with 0 to 1 perineural oligodendrocyte1 per neuron (H&E). (L) Cerebral cortex in 4H patient with a few Olig2-reactive oligodendrocytes; compare with (J). (M) Centrum semiovale in 4H patient. CD68-immunopositive macrophages/microglia are interspersed in the white matter. (N) Centrum semiovale blood vessel in 4H patient, with CD68-positive macrophages adherent or invested in perivascular adventitia or basement membrane. There are a few macrophages in the Virchow-Robin space. (O) CD68-immunoreactive macrophages in 4H patient within the endothelial layer or basement membrane layer of a microvessel. (P1–P4) In the 4H patient, CD68-positive macrophages extend toward (P1), encroach upon (P3) and partially (P2) encircle or completely encircle (P4) oligodendrocytes with clear perinuclear cytoplasm. (Q) CD68-positive macrophages with abundant cytoplasm are closely apposed to 2 oligodendrocytes in the 4H patient (original magnification 40x, CD68). (R) The vast majority of CD68 reactivity in the 4H patient is in macrophages associated with blood vessels. Only rare CD68 reactivity outlines oligodendrocytes (cell with clear cytoplasm) indicating current or prior interaction with macrophages or microglia. These features were not seen in the control. Original magnifications: A, C–E, G, M, N, 10x; B, F, H, I–L, O, 20x; P–R, 40x.