Fig. 1.

CD8⁺ and CD4⁺ T cells populate the human brain. a Gating procedure applied to analyze brain CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells, eluted from normal-appearing white matter. b Quantification of the CD8⁺/CD4⁺ T-cell ratio. Immunohistochemical staining of CD8- (c, d) and CD4- (e, f) immunoreactive cells in normal subcortical white matter of a donor without brain disease. c, e Overview of 10 × 10 tiled images at 10× magnification; the marked square indicates a bright field. d, f 20× magnification (scale bar = 20 µm). g Quantification of CD8-immunoreactive and CD4-immunoreactive cells (number/mm²). h–k Immunofluorescent staining of CD8 (green), laminin (red), and Hoechst (blue) at 10× magnification (scale bar = 50 µm) (h, j) and a zoom-in (i, k). l Quantification of CD8-immunoreactive cells co-localizing with laminin (perivascular space) or not co-localizing with laminin (parenchyma). Bars show median values. p-values show Mann–Whitney U test