MAPT and Alzheimer disease: Interestingly, after inoculation of human tau oligomers, the MC1 epitope was observed in the hippocampus and EC before phosphorylation of tau protein at the AT8 epitope, consistent with data showing that human tau oligomers lead to the formation of an increased level of the aggregated form of tau protein and that the conformational change of tau protein precedes the formation of PHFs, which is one of the earliest pathological changes of tau protein in AD [77,101,102].