TREM2 and Alzheimer disease: TREM2 positive microglia cluster around extracellular plaques in brains of human AD cases and amyloid precursor protein (APP) transgenic mice, and the deletion of TREM2 in APP mouse models  results in  altered morphology and seeding of plaques, as well as decrease in number of plaque associated microglia [28, 51, 67], indicating an involvement of TREM2 in the restriction of Aβ deposits [11, 75].