In TauPS2APP mice, an AD mouse model that combines β-amyloid and Tau pathologies, we found that microglial phagocytosis of synapses near plaques is impaired in the absence of the AD risk gene Trem2. In TauPS2APP;Trem2KO brains, astrocytes compensate for microglial dysfunction around plaques through increased eating of inhibitory synapses. The gene discussed is TREM2; the disease is Alzheimer disease.