Figure 1. Trem2 deficiency affects aging-dependent expansion of microglia.

(A) Microglial numbers were counted as Iba-1⁺ cells per high-power field (HPF) in the corpus callosum, cerebellum, hippocampus, and cortex in mice at 6 months, 1 year, and 2 years after birth. Brain regions analyzed are shown in the corresponding drawings. (B) Representative images of Iba-1⁺ cells in WT and Trem2^–/– mice at different ages. cc, corpus callosum. (C and D) Steady-state microglia in aged Trem2^–/– mice show deramified morphology compared with microglia of age-matched WT mice. (C) Representative images of Iba-1⁺ cells in 2-year-old WT and Trem2^–/– mice. (D) Quantification of microglial surface area (in μm²) visualized by Iba-1 staining. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001, 2-way ANOVA. Original magnification, ×20 (B); ×60 (B, insets; C). Scale bars: 100 μm (B); 30 μm (B, insets; C). Data represent 5 to 10 mice (A and B) and 4 mice (C and D) for each group from a total of 2 experiments. An average of 10 HPF per mouse were evaluated in A. An average of 50 cells in 10 HPF per mouse were evaluated in D. Error bars represent mean ± SEM.