As 4R tau is increased in the NFTs isolated from AD patients [31], [32], and the human tau40 (2N/4R, the longest isoform of human tau) transgenic mice recapitulate features of known neurodegenerative diseases, including AD and other tauopathies [33], we expressed tau40 in cultured rat microglial cells by transient transfection to study the role of tau in microglia during aging in vitro and demonstrated that expression of tau40 induced increasing of Iba1, indicating microglial activation. The gene discussed is MAPT; the disease is Alzheimer disease.