Brain leukocyte subpopulations differ between SHR and WKY. Brains of SHR and WKY contained comparable numbers of CD45 high leukocytes while the composition of subpopulations was strongly different (A). NK cells constituted the predominant immune cell type in SHR. By contrast, the proportion of T cells and monocytes/macrophages (Mo/Mɸ) was higher in WKY. Absolute counts of Mo/Mɸ were decreased (B) whereas NK cells were significantly increased in brains of SHR (C). Immunofluorescence analysis revealed that CD161 positive NK cells (green) were exclusively located in the brain microvasculature (visualized by solanum tuberosum lectin, STL; red) of SHR. Data are mean ± SD. *p < 0.05 by t-test for n = 3 animals/group, scale bar: 10 μm. PMN, polymorphonuclear granulocytes.