C1q and C3, upregulated in human AD brain tissues and CSF [84, 85] as well as in aged AD transgenic mice [86, 87] may opsonize synapses in the presence of oligomeric Aβ for removal by microglia [16, 88], as exposure of microglia in adult mice to oligomeric Aβ induced a significant increase in microglia-mediated engulfment of synaptic material [16]. This evidence concerns the gene C3 and Alzheimer disease.