TREM2 and Alzheimer disease: Importantly, TREM2 haploinsufficiency or TREM2 knockout strongly reduces or no longer allows, respectively, microglial proliferation and microgliosis to occur around brain Aβ plaques; contrariwise, it lessens or prevents microglial activation and induces microglial apoptosis in APPswe/PS1-21 and 5XFAD AD-model mice [90,99].