Immune cell localization in parenchymal and ventricular compartments in the brain of control rat. (A) Leukocytes are preferentially associated with the CPs (illustrated here in the fourth ventricle). A high magnification is shown in the insert. (B) Leukocytes in brain parenchyma are CD68+ cells associated with perivascular spaces. Blood vessels are visualized by laminin. (C) Occasional cells not associated with blood vessels are seen in a subependymal position. Scale bar, 50 μm. 3 V, third ventricle; ep, ependyma; Lm, laminin.