TREM2 and Alzheimer disease: Indeed, accumulating experimental, genetic, and epidemiological data implicate the innate immune system in AD, most prominently involving genes for immune receptors or immune-related functions such as APOE (apolipoprotein E), CR1 (complement receptor 1), B1N1 (bridging integrator 1), CD33, TREM2 (triggering receptor expressed on myeloid cells 2), and PICALM (phosphatidylinositol binding clathrin assembly protein).