Figure 1.

Oxidized DNA in multiple sclerosis lesions, visualized by immunocytochemistry for 8-hydroxy-d-guanosine (8-OHdG). (a) Actively demyelinating lesion in a patient with primary progressive multiple sclerosis; the figure shows areas of the normal-appearing white matter (NAWM) (left), the zone of ongoing demyelinating activity with profound microglia activation and macrophage infiltration (brown immunoreactivity for the macrophage marker CD68) and the inactive portion of the lesion with low macrophage infiltration. Oxidized DNA (8-OHdG) reactivity is shown as blue nuclei, which are mainly present in the active lesion edge (×60). EA = early active demyelination with macrophages containing myelin-reactive degradation products; initial = initial stage of demyelination with profound microglia activation and oligodendrocyte apoptosis; LA centre = late active stage of demyelination in lesions centre; macrophages with neutral lipid degradation products. (b) Higher magnification of the ‘initial’ stage of the active plaque in a, shows profound microglia activation (brown cells; CD68 positive) and many blue nuclei, representing cells with DNA oxidation; the asterisks in a and b indicate the position of b within the lesion shown in a (×200). (c) Normal white matter of a control patient without neurological disease and brain lesions; only very few microglia cells show cytoplasmic CD68 reactivity (brown); there are no blue nuclei, suggesting DNA oxidation (×100). (d) Normal-appearing white matter (NAWM) of a patient with acute multiple sclerosis (Marburg’s type); similar pattern as in the control white matter, shown in c (×100). (e) Very early active lesion area in a patient with acute multiple sclerosis (Marburg’s type); profound microglia activation (brown cells; CD68) adjacent to cell nuclei, positive for 8-hydroxy-d-guanosine (blue) (×100). (f) Late active lesion centre in a patient with Marburg’s type of acute multiple sclerosis; numerous CD68-positive macrophages (brown), but no nuclei with blue 8-hydroxy-d-guanosine reactivity (×100). (g) Double staining for oxidized DNA (8-hydroxy-d-guanosine; blue) and the oligodendrocyte marker TPPP-p25 (red) at the lesion edge of an active lesion of acute multiple sclerosis. One of the six oligodendrocytes shows blue 8-hydroxy-d-guanosine reactivity in a nucleus with nuclear condensation and fragmentation (apoptotic cell) (×900). (h) Double staining for oxidized DNA (8-hydroxy-D-guanosine, blue) and glial fibrillary acidic protein (GFAP, red) at the edge of an active lesion of acute multiple sclerosis. One astrocyte contains a blue nucleus, indicating oxidized DNA (×600). (i) Double staining for oxidized DNA (8-hydroxy-d-guanosine, blue) and the macrophage marker CD68 (red) in an active lesion of acute multiple sclerosis. The macrophage contains a nucleus with oxidized DNA, possibly representing phagocytosis of an apoptotic cell (×600). (j) Double staining for oxidized DNA (8-hydroxy-d-guanosine, blue) and the T-cell marker CD3 (red) in an active lesion of acute multiple sclerosis. No DNA oxidation is seen in the CD3-positive T-cell population (×200).