TREM2 and Alzheimer disease: Notably, TREM2 plays important roles on microglial functions such as phagocytosis, biosynthetic metabolism, and inflammatory response (Condello et al., 2018), and TREM2 deficiency exacerbates activated M1 microglial inflammatory cytokines release and neuronal apoptosis, but TREM2 overexpression markedly attenuated inflammation and neuronal death in AD model studies (Jiang et al., 2014; Jay et al., 2015, 2017).