SUBPOPULATIONS OF DYSTROPHIC NEURITIS IN ALZHEIMERS BRAIN WITH DISTINCT IMMUNOCYTOCHEMICAL AND ARGENTOPHILIC CHARACTERISTICS

Using two monoclonal antibodies, tau-l and PHF-1, and a sequential sta ining method combining double-labeling immunofluorescence and Bielscho wsky silver staining, we have demonstrated the presence of two populat ions of dystrophic neurites (DNs) with distinct immunocytochemical and argentophilic characteristics. Tau-1 and PHF-1 immunoreactivity were co-localized in many DNs. However, approximately 20% of the DNs were i mmunoreactive for PHF-1 only. PHF-1 single-labeled DNs were not visibl e or very weak with Bielschowsky silver stain. Of DNs continuous with neurofibrillary tangles (NFTs), tau-1/PHF-1 double-labeled DNs were co ntinuous with intracellular NFTs only, while PHF-1 single-labeled DNs were continuous with extracellular NFTs only. Furthermore, the populat ion of DNs that cluster around extracellular NFTs is different from th ose that cluster around or within senile plaques. The combined use of tau-1 and PHF-1 immunocytochemistry may provide a more accurate indica tion of the number of extracellular DNs and extracellular NFTs, which may aid in the diagnosis of severe and advanced AD cases.