Studies have found that elevated levels of inflammation-related features are detected in the cerebrospinal fluid and serum in patients with MCI and AD patients [e.g., YKL-40, interleukin (IL)-8, TREM2, and monocyte chemotactic protein-1 (MCP-1)] (Bowman et al., 2018; Nordengen et al., 2019). Here, TREM2 is linked to Alzheimer disease.