Figure 5. CSF-circulating DCs infiltrate the brain parenchyma.

Fluorescent microspheres or DCs labeled with the cytoplasmic fluorescent marker CFSE were injected into the left lateral ventricle of EAE rats (n = 32) at the clinical peak of disease (day 12 post-immunization). EAE rats injected with fluorescent microspheres (n = 14) or CFSE-labeled DCs (n = 18) were then sacrificed on day 1 post-injection (n = 16) and their brains examined by immunohistology using antibodies directed against CD11b/CD11c (OX42) or MHC class II molecules. Nuclei were counterstained with the fluorescent nuclear dye DAPI. A–C: Visualization of nuclei with DAPI coloration (A) allows the localization of microspheres (white in B, red in C) to be determined (dashed squares in A and B). Microspheres are detected in the molecular layer of the cerebellum and localize in the cytoplasm of a MHC class II⁺ cell (C). Insert in C shows a high magnification view of this microspheres⁺/MHC class II⁺ cell. DAPI coloration (A) and MHC class II staining (C) shows that there is no detectable inflammatory infiltrate in this area of the cerebellum. D–F: In the brainstem, an intraparenchymal inflammatory infiltrate is formed by OX42⁺ cells (D) and contains a CFSE⁺ cell (E) that expresses OX42 (F). G–I: In the brainstem, an area of diffuse infiltration with OX42⁺ cells (G) contains a CFSE⁺ cell (H) that expresses OX42 (I). Inserts in G, H and I show high magnification views of this CFSE⁺/OX42⁺ cell. Scale bars: 100 µm (A, B), 50 µm (C–I), 10 µm (insert in panel C).