Distinctive localization of immune cells in the CNS of EAE-diseased rats. (A to K) CD45+ immune cells in the forebrain. (L to O) CD45+ cells in the hindbrain. (A) CD45+ cells are visualized in a subependymal location at D9. (B) (D9), (C to F) and (L to N) (D11). CD45+ cells are observed in certain periventricular areas. Cells often infiltrate the tissue as clusters in the habenula (B), ventrally to the corpus callosum (C), in the hippocampal alveus close to the lateral ventricle (D), in the pons along the fourth ventricle (L) and its recesses (M). Cells infiltrate the tissue in a disseminated manner following a downward density gradient from the CSF to the parenchyma (B,M, arrowheads) or along perivascular spaces close to the ventricle, for example in the fimbriae (E), and in the fourth ventricle (M,N, arrows). There are no cells around vessels in deeper structures such as the hippocampal fissure (star in (F)) and the pons (star in (N)). Laminin (lm) stains the basal membrane of the vessels. In (N) the upper side of the image is facing CSF; the lower side is deep pons tissue. (G to K) By D11, the number of leukocytes has increased in extraventricular CSF-containing internal compartments such as the velum interpositum (G, J) and ambient cisterns (H, K) and also in more peripheral cisterns such as the cistern of the laminae terminalis (I). The insert in (G) shows a high magnification of CD45+ cells in the velum interpositum space. Some infiltrates are localized between the third ventricle and the cistern of the velum interpositum (G, white arrowhead). Cell infiltrates displaying a downward CSF to tissue density gradient are found ventrally to the velum interpositum (arrowhead in (J)) or along perivascular spaces adjacent to extraventricular CSF-filled compartments (J, K, arrows). (O) In spinal cord leukocytes massively infiltrate the meninges and adajcent perivascular spaces (arrow). They also disseminate in the parenchyma, dorsally to the central canal. Scale bar, 20 μm (A to L), 50 μm (M to O). Dashed lines delimit ventricles (C, M) or cisterns (G to K). 4VCP, fourth ventricle choroid plexus; ACi, ambient cistern; Cb, cerebellum; cc, corpus callosum; CCa, central canal; CiLT, cistern of the laminae terminalis; ep, ependyma; fi, fimbria; Hb, habenula; Hip, hippocampus; HipV, hippocampal vessels; IC, inferior colliculus; LS, lateral septum; LV, lateral ventricle; LVCP, lateral ventricle choroid plexus; SC, superior colliculus; Ve, vestibular nucleus (pons); VI, velum interpositum cistern.