There is evidence that TREM2 is protective (Zhao et al., 2017; Brown and St George-Hyslop, 2021) as is soluble TREM2, which binds Aβ, prevents its oligomerization and improves cognition in a mouse model of AD (Zhong et al., 2019; Sheng et al., 2021). Here, TREM2 is linked to Alzheimer disease.