Immunocytochemical evidence that the β-protein precursor is an integral component of neurofibrillary tangles of Alzheimer's disease

Amyloid β (Aβ) immunoreactivity has been demonstrated in all extracellular neurofibrillary tangles (E-NFT) and most intraneuronal neurofibrillary tangles (I-NFT). We undertook this immunocytochemical study to understand the relationship between Aβ immunoreactivity localized in NFT and β-protein precursor (βPP). We found epitopes of amino-, mid-, and carboxyl-terminal domains of βPP in I-NFT and the majority of E-NFT. NFT retained βPP after ionic detergent extraction, demonstrating that βPP is an integral component of NFT. Finding βPP in regions of Aβ immunoreactivity raises the possibility that βPP or its fragments associate with amyloid, and that the stability of Aβ is responsible for its dominance in amyloid deposits.