TREM2 and Alzheimer disease: Opposite results were described in vivo, as an increased expression of TREM2 was observed both in microglial cells and in hippocampus of post-mortem brain of AD patients [89,90,91] and in mouse models of amyloid and tau pathology [85,92,93,94,95], possibly being associated with the recruitment of microglia into amyloid plaques [94,95,96,97].