Fig. 6

Microglia ablation in APP-PS1 mice resulted in increased CD3⁺/CD8⁺ T-cell numbers in the brain, and CD8⁺ T-cell numbers were highly increased in cortical brain regions of APP-PS1 mice interacting with Iba1⁺/TMEM119⁺ and Iba1⁺/TMEM119⁻ cells. Detailed immunohistochemical analysis of CD8⁺ T-cell numbers (green) in brains of APP-PS1 mice revealed similar CD8⁺ T-cell numbers compared to WT when analyzing total sagittal brain sections; however, CD8⁺ T-cell numbers were significantly increased in cortical brain regions of APP-PS1 mice compared to WT (a). T-cells were mechanically isolated from total brain hemispheres and quantitatively analyzed by flow cytometry after ablation of microglia cells (b, gated for single-living CD45⁺/CD3⁺ cells; CD4⁺ red, CD8⁺ green). The total number of CD45⁺/CD3⁺ T-cells was significantly increased in APP-PS1 mice treated with PLX5622 compared to WT-treated mice (c). CD3⁺/CD4⁺ T-cell numbers trend to be increased in APP-PS1 mice treated with PLX5622 (d). CD3⁺/CD8⁺ T-cell numbers were significantly increased in APP-PS1 mice treated with PLX5622 compared to APP-PS1 and WT PLX5622-treated mice (e). CD8⁺ T-cells in APP-PS1 mice were located directly in the brain parenchyma and observed in different interaction types with Iba1⁺ cells (white), showing either no contact, intermediate, or very tight interaction with brains Iba1⁺ cells (f). Performing confocal microscopy, we observed very tight cell to cell interactions with Iba1⁺ cells (g) and orthogonal projections showed CD8⁺ T-cells associated with Iba1⁺/TMEM119⁺ and as well with Iba1⁺/TMEM119⁻ cells in APP-PS1 mice (arrow, h). CD8⁺ T-cells that tightly associated to Iba1⁺ cells showed high expression of Zap70 (red) at sites of the cell membrane, indicating immune synapse formation, and activation of the T-cell receptor complex (arrow, i). Dapi (blue) was used as nucleus stain. One-way ANOVA with Tukey’s multiple comparison test (c, d, e n = 8–9/group) and unpaired Student’s t test (a, n = 5/group) was performed. Scale: 1 mm and 50 μm (a), 20 μm (f), 10 μm (h, i), 5 μm (g)