Macrophages and microglia express CD47 and SIRPα whereas myelin, Schwann cells, oligodendrocytes and astrocytes express CD47 without SIRPα. Macrophages (MO) express (A) Galectin-3, cell surface (B) SIRPα, and (C) CD47. (D) Macrophages phagocytose myelin. F-actin (filamentous actin) is visualized by Alexa 488 labeled phalloidin (green) and myelin by anti-MBP mAb (red); overlap between the two is yellow. Myelin is present in the cytoplasm interior to cortical F-actin. Similar observations were made in microglia (not shown; see ). Microglia (MG) express (E) Galectin-3, and cell surface (F) SIRPα and (G) CD47. (H) MBP and (J) CD47 are expressed in myelin without (I) SIRPα. (K) Anti-Fc-Fab2 fragments coat/block Fc-segments of anti-CD47 mAb that binds CD47 on myelin, thus preventing visualization of anti-CD47 mAb by a secondary Ab. (L) CD47 is expressed on spindle shaped bipolar Schwann cells (arrow) and flat fibroblasts (double arrow). (M) CD47 is expressed on oligodendrocytes (arrow) that extend elongated branched processes, and on flat astrocytes (double arrow). Galectin-3, CD47, SIRPα and MBP are visualized by immunofluorescence confocal microscopy using respective mAbs directed against each (red). Bars are 5 μm in A through K, and 50 μm in L and M.