Traffic of microsphere-loaded DCs in the CNS of normal rats. DCs were incubated for 24 hours with fluorescent microspheres, then washed and injected into the CSF (A-G) or brain parenchyma (H) of normal rats. Photomicrographs show representative results obtained from analyses of brains on day 3 after injections. (A-D) Brain sections were examined by light microscopy after hematein-eosin staining (A,C) or by fluorescent microscopy to detect cells loaded with fluorescent beads (red) (B,D). Groups of labeled cells are detected in the lateral ventricle, homolateral to the injection site, on the apical surface of the choroid plexus (A-B; circle). Injected DCs are detected bilaterally in the recesses of the fourth ventricle (C-D). (E-G) For the detection of cells loaded with red fluorescent beads, brain sections were examined by fluorescence microscopy after counterstaining with DAPI for nuclei visualization (blue). Cells loaded with fluorescent beads are observed in the subventricular zone homolateral to intravenous injection and particularly within the germinal zone (E-F; circles). Inset in panel F shows a high magnification view of a cell located in the germinal zone and harboring numerous intracytoplasmic beads. Photomicrograph in panel G shows a cell containing fluorescent beads in brain parenchyma adjacent to the third ventricle. (H) DCs loaded with fluorescent microspheres and injected into the corpus callosum migrate a short distance from the injection site, along the adjacent white matter tracts. LV indicates lateral ventricle; cc, corpus callosum; CP, choroid plexus; Ce, cerebellum; V3, third ventricle. Scale bars: 200 μm (C,D,H), 100 μm (A,B,E,F), 50 μm (G), 2 μm (inset in panel F).