Distinctive localization of immune cells in the CNS of EAE-diseased mice. (A) Localization of leukocytes in the brain of control mice. Leukocytes are mainly CD68+ monocytic cells and preferentially localize in basal and internal cisterns of the brain such as the ambient cistern. (B,C) Increase in leukocyte number in the brain of PI animals. At P10-14, the number of CD68+ cells slightly increases in these CSF compartments (B), and some leukocytes, including CD3+ T cells infiltrate the hippocampus (C). (D to O) Immune cell infiltration in the brain of EAE-diseased animals. (D, F, H, L) are from animals with a clinical score of 1, and (E, G, I to K, M to O) are from animals with a clinical score of 4. Similar observations were made for both scores. The number of CD68+ cells increases drastically in the extraventricular CSF compartments such as the cisterns of the optic tract (D), the interpeduncular and ambient cisterns (E), and the velum interpositum space (K). Leukocytes in extraventricular spaces spread rostrally to the cistern of the laminae terminalis (F). CD3+ T cells and MPO+ neutrophils are also present in these spaces (F, dashed insert in F, J, K). Immune cells infiltrate the parenchyma in subependymal locations (G), and in forebrain and midbrain structures in close proximity to the CSF (H, J, K, L). On the caudal side, infiltrates reach the structures that border the lateral recesses of the fourth ventricle such as the inferior cerebellar peduncles (I). Tissue infiltration occurs following a downward CSF-to-tissue gradient (arrowhead in H and I) or along perivascular spaces (arrow in J and L). Tissue infiltrates are composed mainly of CD3+ (J) and CD68+ cells (H, I, K). To a lesser extent MPO+ cells are also present (H, I, K). The mouse EAE model is characterized by the additional infiltration of CD68+ and CD3+ cells in the white matter of the corpus callosum (L) and of the cerebellum (M). B cells are found in CSF-filled cisterns (N) in the same proportion as T cells, but do not invade the parenchyma as do CD3+ cells (O). In (A, C, K, L) inserts show high magnifications of immune cells in the areas of interest. Scale bar, 50 μm (A-H, J-O), 100 μm (I). 3 V, third ventricle; 4VCP, fourth ventricle choroid plexus; ACi, ambient cistern; Cb, cerebellum; cc, corpus callosum; CiLT, cistern of the laminae terminalis; CiOT, cistern of the optic tract; fi, fimbria; Hb, habenula; Hip, hippocampus; Hypo, hypothalamus; icp, inferior cerebellar peduncle; LS, lateral septum;LV, lateral ventricle; SFO, subfornical organ; VI, velum interpositum cistern.