Fig. 4

Immunogold labelling of tau filaments from human AD brain. Representative electron microscope images of tau fibrils isolated from the sarkosyl-insoluble fraction of AD patient frontal cortex. E2814 or IgG1 isotype control were used at 10 μg/mL. Tau 5 antibody was used at 0.4 μg/mL. Bound antibody was detected following addition of an anti-human 12 nm gold conjugated antibody at 1:25 dilution or an anti-mouse 6 nm gold conjugated antibody at 1:25 dilution (for Tau 5). a, b: E2814 could bind the entire length of many tau fibrils. In some paired helical filaments (PHFs) E2814 binding was limited to the ends (arrows) of the fibrils (c) or was completely absent (d). f: E2814 (arrows) and the commercially available Tau 5 antibody (arrowheads) co-stain tau fibrils, providing proof of E2814 specificity to tau fibrils. g: Tau 5 binds to the entire length of tau fibrils. h: E2814 specifically binds to smaller structures on the EM grids that may represent tau fibril fragments or tau oligomers (arrows). The IgG1 control antibody did not bind to filbrils (e), or smaller fragments (f). j,k). Pre-treatment of AD fibrils with 0.4 mg/ml pronase removed the fuzzy coat of PHFs and SFs, leaving the structured core intact with E2814 staining retained only at some fibril ends (Scale bars = 200 nm)