TREM2 and Alzheimer disease: Microglia in TREM2-deficient AD mice display less activation and do not engulf Aβ plaques, which reduces the density of Aβ plaques and promotes diffuse Aβ structures, which, in turn, are more neurotoxic and contribute to the accumulation of classic AD pathology (Wang et al., 2016; Yuan et al., 2016).