Fig 1: Characterizing microglial activation with MEC AAV-tau transduction. A MEC and DG regions from WT or Trem2 KO mouse brain 5 weeks following AAV-tau injection. Sections were stained for AT8 (originally green, shown in purple), Cd68 (originally purple, shown in green), P2y12 (red) and nuclei (DAPI, blue), magnified regions are shown for Cd68/P2y12 colocalization. Bar = 50 μm. B Quantification of percentage P2y12 (top graphs), Cd68 (middle graphs) or P2y12/Cd68 double-positive microglia (bottom graphs) in the MEC region (left graphs) or DG (right graphs) from WT and Trem2 KO brain (n = 8 animal/genotype). C MEC and DG regions from WT or Trem2 KO mouse brain 5 weeks following AAV-tau injection. Sections were stained for AT8 (originally green, shown in purple), Iba1 (originally purple, shown in green), CD9 (red) and nuclei (DAPI, blue), magnified regions are shown for Iba1/CD9 colocalization. Bar = 50 μm. D Quantification of relative CD9 intensity (compared to WT, set to 1.0), or % CD9/Iba1 double-positive microglia in MEC or DG regions as indicated from WT and Trem2 KO brain (n = 8 animal/genotype). E MEC and DG regions from WT or Trem2 KO mouse brain 5 weeks following AAV-tau injection. Sections were stained for AT8 (originally green, shown in purple), Clec7a (originally purple, shown in green), Tmem119 (red) and nuclei (DAPI, blue), magnified regions are shown for Clec7a and Tmem119 colocalization. Bar = 50 μm. F Quantification of % Tmem119 positive (top graphs), Clec7a-positive (middle graphs), or Tmem119/Clec7a double positive (bottom graphs) microglia in MEC or DG regions as indicated from WT and Trem2 KO brain (n = 8 animal/genotype). In (B, D and F), graphs represent mean ± SE from WT and Trem2 KO brain (n = 8 animal/genotype). Statistical significance was determined using unpaired Student’s t-tests (**p < 0.01, ***p < 0.001, **** p < 0.0001)