Figure 7. Histological features of MS lesions with phase rim.

Chronic demyelination colocalizes with the phase rim at the lesion edge. There are no signs of ongoing remyelination and only rare oligodendrocyte precursor cells (OLIG2⁺/ASPA^– cells, red arrows). In a cortical lesion, on the other hand, there is evidence of oligodendrocyte precursor cells as well as remyelination. Macrophages/activated microglia also colocalize with the phase rim at the lesion edge. Luxol fast blue (cyan) and lipofuscin (purple) inclusions within these cells suggest ongoing early and late myelin degradation process (×100 magnification). A rim of iron-laden CD68-positive cells are clearly present at the lesion edge (DAB-Turnbull staining alone and double staining with anti-CD68/DAB-Turnbull). Mature tissue macrophages expressing the scavenger receptor CD163 were also represented in the CD68 population, suggesting that the population was not homogeneous (double staining with CD68/CD163). Reactive astrocytes and axonal damage: Non–iron-laden reactive astrocytes were seen in the demyelinated lesion center and demyelinating lesion edge (double staining with GFAP/DAB-Turnbull). Residual axons within the lesion center showed evidence of impaired axonal transport (positive staining for nonphosphorylated neurofilaments expressing SMI32). Red arrows indicate the presence, at the lesion edge, of sparse SMI32-positive ovoids suggesting ongoing axonal degeneration. Scale bars: 50 μm (top row); 10 μm (left panel, middle row); 50 μm (right 3 panels, middle row); 50 μm (left 2 panels, bottom row); 20 μm (right 2 panels, bottom row).