(A) Schematic of 2N4R tau with N-terminal inserts (N1 and N2) and microtubule-binding repeats (R1, R2, R3, R4) highlighted. The epitopes of antibodies BR133 (residues 1–16), BR136 (244-257), Anti4R (275-291), BR135 (323-335), TauC4 (354–369) and BR134 (428-441) are underlined. (B) Representative immuno-EM images with antibodies BR133, BR136, Anti4R, BR135, TauC4, and BR134 of heparin-induced 2N4R and 2N3R tau filaments without (-) and with pronase (+) treatment. Scale bar, 100 nm. (C) Table summarising the results from B, and comparison with the immuno-EM results of AD and PiD. Tick marks indicate antibody decoration of filaments; crosses indicate absence of decoration. The four boxes where the human diseases differ from the in vitro heparin-induced filaments are highlighted in blue.