Phosphorylation state of tau in the CNS of single Tg and bigenic mice. Immunoblots were performed using PHF tau from AD brain, autopsy-derived normal human adult tau and autopsy-derived human fetal tau samples, as well as soluble and insoluble fractions of tau from the neocortex of 12-month-old T44 Tg, T44 Tg;NFL−/−, and T44;NFH−/− mice. Antibodies 17026 and T14 recognized total tau proteins regardless of the phosphorylation state. Antibody T1 was specific to nonphosphorylated tau and did not react with PHF-tau. Phosphorylation-dependent antibodies PHF1, T3P, and AT270 did not recognize normal adult tau but reacted with PHF-tau and fetal tau, as well as both soluble and insoluble fraction of tau from the single Tg and bigenic mice.