Cell associated C3b complement staining. Paraffin wax section of active peri-plaque regions (A, case MS377_S2; B, case MS383_21) immunolabelled with anti-C3b showing cells with astrocytic morphology. Myelin degradation debris (arrows) within macrophages colabelled with anti-C3b (brown) and MOG (grey) are shown within the centre of an active plaque (C, MS160_S3). Immunofluorescent staining: D1 (case MS 225_S13, chronic active plaque) and D2 (case 377_S2, active plaque) showing colabelling of C3b (red) and GFAP + astrocytes (green) in the peri-plaque white matter. E1 (case MS225_S13, chronic active plaque; plaque (P) and peri-plaque (PP)), E2 and E3 (both case MS377_S2, active plaque) show zones of HLA-DR macrophages/microglia and an adjacent area of predominantly astrocytic and axonal C3b immunolabelled structures. In figure E3, note the close approximation of C3b positive axon (arrow) and HLA positive microglial cell. F shows an anti-C3b positive myelin strand (brown, arrow) co-localised with MOG (grey) on an axon bundle within striatum (case MS160_S3, active plaque). Immunofluorescent staining (G), showing anti-C3b immunopositive myelin (red) co-localised with an anti-SMI-32 (green), immunopositive non-phosphorylated axon at the edge of a chronic active white matter lesion (case MS160_S3, active plaque). Scale bars are shown for each slide.