Recent studies have disclosed AD-related alterations in the genetic and functional profile of microglia, the immune-competent cells in the brain, and association of mutations in microglia-specific genes (e.g. TREM2) with AD, which triggers an escalating interest in microglia, particularly microglia-mediated neuroinflammation, and recognition of its importance in AD pathogenesis and progression (McQuade and Blurton-Jones, 2019; Wang and Colonna, 2019). Here, TREM2 is linked to Alzheimer disease.