Fyn KO-AAV mice displayed less hyperphosphorylated tau relative to WT-AAV injected mice. Using double immunofluorescent labeling, WT-AAV hippocampus showed robust pS199/pT202 (a) and pY18 (d) staining of NFTs in the hippocampal CA1 region. Fyn KO-AAV hippocampus showed only limited pS199/pT202 (b) and pY18 (e) staining of NFTs in the same region. Using adjacent slides from the same mice, staining of pT231 showed robust staining in WT-AAV CA1 (g) but fewer NFTS in CA1 of Fyn KO-AAV (h). Intensity was determined as described in Methods (four fields from each of six animals) and p values calculated by t-test. Relative to WT-AAV, Fyn KO-AAV had reduced staining for pS199/pT202 (c, p = 0.0035), pY18 (f, p < 0.0001) and pT231 (i, p = 0.0037). Analysis was carried out using 4 random pictures taken from the hippocampus of 3 WT-AAV and 3 Fyn KO-AAV mice. Representative images were shown. Scale bar: 25 μm.