Tau multimers were measured using the same HT7 antibody for capture and detection in a single-epitope immunodetection design that cannot detect monomeric tau forms (Fig. 4d). When measuring HT7/HT7 tau multimers, we made very similar observations (compare Fig. 4c with d), highly correlated with the levels of the MC1 signal (Fig. 4d,e). Again, while aggregated tau remained stable in the AAV-WT group of mice, a progressive accumulation of tau multimers occurred in the forebrain of the AAV-P301S group. Compared to WT tau, the level of P301S tau multimers was increased by 3.1- and 3.3-fold at 3 and 7 months post-injection, respectively. Overall, we find a prominent effect of the P301S mutation on the misfolding and aggregation of the tau protein in vivo.