T cell compartmentalization and morphology is different in SHR. Absolute T cell counts were significantly lower in brains of SHR (A). Histological analysis of T cell distribution in both strains revealed that only 20% of total T cells in SHR resided in the meninges and the choroid plexus (CP), while the remaining cells were located in parenchymal microvessels (B). This distribution was reversed in WKY. (B) shows representative sections of the meninges in SHR and WKY. T cells were identified by the pan T cell marker 15-16A1 (green). Distinct T cell compartmentalization was accompanied by a decrease of IL-10, but similar levels of IFNγ in the cerebrospinal fluid (CSF) of SHR (C). Numbers of intravascular T cells neither differed in the total brain nor in the deep cortical region (DCR) (D). In SHR, two-thirds of all T cells were rod-shaped while the rod-to-round ratio was almost 1:1 in WKY (D). Representative images of rod and round shaped T cells (green) in brain microvessels (visualized by solanum tuberosum lectin, STL; red). mRNA expression of vascular adhesion molecule 1 (VCAM-1) was significantly increased in brain endothelial cells of SHR (E). Data are mean ± SD. *p < 0.05, **p < 0.01, ***p < 0.001 by t-test for n = 3 (A), n = 4 (B, C and D) or n = 5 (E) animals/group, scale bar: (B) 20 μm; (D) 5 μm.