Tau oligomers derived from PSP brain seed aggregation of 3R and 4R tau. AFM image of tau oligomers immunoprecipitated from PSP brain and 3R and 4R tau seeded with PSP BDTO display characteristic oligomeric structure and size (a). Scale bar 50 nm. Western blot with Tau-5 shows oligomeric tau present in both 3R and 4R tau seeded with PSP BDTO (b). Direct ELISA with Tau-5 shows consistent tau levels in 3R and 4R tau monomer seeded with PSP BDTO and increasing levels of tau oligomers as incubation time with oligomeric tau increases (c).