TREM2 and Alzheimer disease: Additionally, soluble TREM2 (sTREM2) is a potential AD biomarker (Brosseron et al., 2020) and can be detected in cerebrospinal fluid (CSF) in both healthy individuals and AD patients (Carmona et al., 2018), elevated sTREM2 levels noted in the CSF of AD patients (Yang et al., 2020).