TREM2 and Alzheimer disease: To determine whether phagocytosis within microglia due to device injury is elevated around implanted microelectrodes or within AD, explanted WT and APP/PS1 brain tissue were stained for Iba-1, a microglial marker, and ‘triggering receptor expressed on myeloid cells 2ʹ (TREM2), an innate immune receptor predominantly expressed by microglia within the brain during conditions of metabolic stress [25].