Peptide Competition: Background extracts spiked with human recombinant tau left untreated (5) or treated with GSK-3 beta to become phosphorylated (1-4) were resolved by SDS-PAGE on a 10% polyacrylamide gel and transferred to PVDF. Membranes were blocked with a 5% BSA-TBST buffer overnight at 4^oC, then were incubated with 0.50 µg/mL ab4846 antibody for two hours at room temperature in a 1% BSA-TBST buffer, following prior incubation with: no peptide (1, 5), the non-phosphopeptide corresponding to the immunogen (2), a generic phosphoserine containing peptide (3), or, the phosphopeptide immunogen (4). After washing, membranes were incubated with goat F(ab’)2 antirabbit IgG alkaline phosphatase and bands were detected using the Tropix WesternStar method. The data show that only the peptide corresponding to ab4846 blocks the antibody signal, thereby demonstrating the specificity of the antibody. The data also show the induction of phosphorylation after treatm