TREM2 and Alzheimer disease: With amyloid-β accumulation, the DAM phenotype arises, and DAMs then surround amyloid plaques in an apolipoprotein E (APOE)- and triggering receptor expressed on myeloid cells 2 (TREM2)-dependent manner (Keren-Shaul et al., 2017; Frigerio et al., 2019); both APOE and TREM2 are well-known AD risk genes (Pimenova et al., 2018).