MAPT and Alzheimer disease: To determine whether 77G7 reacts with the aggregated tau and un‐aggregated tau similarly, we separated tau from AD brain into different fractions, heat‐stable un‐aggregated tau (HS‐tau), oligomeric‐tau (O‐tau), sarkosyl insoluble 1 tau (SI1‐tau), sarkosyl insoluble 2 tau (SI2‐tau) (Figure 1C) and analyzed the immunoreactivity of 77G7 toward them.