We performed paramagnetic bead-based immunoprecipitation (IP) of a pooled TBS-soluble AD brain homogenate using six antibodies together stretching the tau441 sequence (Extended Data Fig. 1a), comparing tau forms in the nondepleted (before IP), depleted (supernatant after IP) and precipitate (immunoprecipitated; tau forms pulled by the antibody of interest and thus enriched on the beads) fractions by MS using a parallel reaction monitoring (PRM) assay on a high-resolution quadrupole Orbitrap hybrid instrument (Orbitrap Exploris 480) online coupled with nanoflow LC. Here, MAPT is linked to Alzheimer disease.