A possible fetal antigen of Mr 70,000 in neurofibrillary tangles

To test the hypothesis that tau-immunoreactive curly fibers represent a regenerative attempt of cortical neurons in the brain affected with Alzheimer's disease (AD), we established 2 monoclonal antibodies to isolated neurofibrillary tangles. Both antibodies extensively stained curly fibers and specifically labeled a novel protein of Mr 70,000 (p70), which was abundantly expressed in fetal brain, but undetectable in adult brain. Furthermore, the antibodies visualized curly fibers in newborn rat brain, which were very similar to those in the AD brain, and also intensely stained extending neurites of NGF-primed PC 12 cells. These observations suggest that P70 is a fetal antigen associated with growing neurites, and thus support the sprouting hypothesis.