MAPT and Alzheimer disease: Each of the three AD-tau preparations underwent dose-response testing in the primary neuronal assay, with insoluble tau pathology imaged after detergent extraction and subsequent fixation of the neurons, followed by immunofluorescence staining with the rodent tau-specific T49 antibody (e.g., Fig. 1D) (27) to establish AD-tau doses that fell within the linear range of tau pathological seeding (Fig. 1B).