Alz 50 recognizes abnormal filaments in Alzheimer's disease and progressive supranuclear palsy.

The monoclonal antibody Alz 50 recognizes a 68-kDa protein present in large amounts in cerebral tissue of patients with Alzheimer's disease (AD). We used light and electron microscopic as well as quantitative immunochemical techniques to compare distribution, characteristics, and amount of Alz 50 antigen in the tegmental nuclei of the pons of subjects with progressive supranuclear palsy (PSP) and subjects with AD. In both conditions Alz 50 antigen was found in neurons with and without neurofibrillary tangles (NFT). In NFT-bearing neurons the antigen was located in the filamentous components of NFT in both diseases, i.e., in straight filaments forming the NFT in PSP and in paired helical filaments components of the NFT in AD. In neurons lacking NFT the antigen was associated with straight filaments of various sizes, but the straight filaments were generally thinner than those of PSP. On immunoblots of both PSP and AD tissues, Alz 50 recognized a set of bands between 68 and 35 kDa which were not present in control tissue. The amount of Alz 50 antigen in AD tissue was estimated to be 10 times higher than that present in PSP tissue. The higher amount of Alz 50 antigen in AD tissue correlates with the more severe fibrillary pathology in this disease than in PSP. We propose that the Alz 50 antigen, although possibly related to tau proteins, distinguishes neurons that are forming abnormal filaments.