Fig. 3
A Klüver-Barrera-PAS (KL-PAS) myelin staining shows a focal, sharply demarcated demyelinated white matter lesion with profound vacuolization. B Immunohistochemistry (IHC) for the oligodendrocyte marker TPPP/p25 reveals preservation of oligodendrocyte cell bodies in the lesion, which were markedly enlarged when compared to surrounding white matter oligodendrocytes. C Same staining as B shows profound enlargement of virtually all preserved oligodendrocytes in the lesion. Note the moderate perivascular lymphocyte cuff in the lesion. D Hematoxylin & Eosin staining reveals round, enlarged oxyphilic oligodendrocytes with distended eosinophilic, finely granular cytoplasm and round, enlarged and dented nuclei, which are frequently pushed to the cell margin. Mitotic figures or apoptoses are not evident. E Immunohistochemistry (IHC) for HLA-DR shows microglia and minor macrophage activation, which was confined to the actual lesion area. F VDAC1 IHC targeted against the mitochondrial porin antigen reveals accumulation of mitochondria in the enlarged glial cells. G Myelin basic protein IHC shows active granular myelin disintegration. Myelin remnants are found in the extracellular space but not within macrophage cytoplasmata. H GFAP staining shows fibrillar gliosis and the absence of immunoreactivity in the enlarged oncocytic glia cells. I CD68 IHC displays microglia and small macrophages in a moderate density. Foamy macrophages can hardly be observed in this lesion. J Electron micrograph presents a glial cell with round nucleus, large cytoplasm and increased numbers of mitochondria (red arrows). K At higher magnification of the glial cytoplasm, the high density of mitochondria is appreciated. L Mitochondria frequently displayed unspecific morphological abnormalities in the form of densely packed cristae. Magnifications: A, B, C, E, G: 200x; D, H, I, Inset in E: 400x; All other insets: 600x; J: 7000x; K: 12000x; L: 20000x