MAPT and Alzheimer disease: The present study reveals that tau antibody 77G7 binds to the four highly homologous and yet independent tetrapeptides located in each microtubule‐binding repeat (MTBR) and has a high affinity to aggregated tau and not un‐aggregated tau derived from AD brain, inhibits the cellular uptake of tau aggregates and suppresses the seeding activity of AD O‐tau to recruit tau and to template tau aggregation in vitro and in vivo in tau transgenic mice.