Trem2 is essential for normal phagocytic activity. (A-B) Effects of Trem2 genotype (WT, Hets, Ko) on ex vivo phagocytic activity in microglia isolated from the hippocampus of 17-day old pups (n = 10–17 pups per group, 50 % females). (C) Representative confocal images (top row) and Imaris models (middle and lower rows) of microglia from Trem2 wildtype (WT), heterozygous (Hets) and knockout P17 littermates. Staining for Iba1 (green), CD68 (blue), and PSD95 (red). Middle row: reconstruction of Iba1 & CD68 staining. Lower row: reconstruction of CD68 and PSD95 staining inside microglia. Effects of Trem2 genotype on microglial volume (D), CD68 volume inside microglia (E), number of PSD95 puncta in microglia (F) and PSD95 puncta inside CD68 (G), n = 5 cells per mouse and 4–5 mice per group, 50 % females). Error bars represent mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.