Two Monoclonal Antibodies Recognize Alzheimer's Neurofibrillary Tangles, Neurofilament, and Microtubule‐Associated Proteins

Abstract: Two monoclonal antibodies that recognize Alzheimer's neurofibrillary tangles (ANTs), AD10 and AB18, have been characterized by immunoblotting against human and calf spinal cord neurofilament (NF) and calf brain mi‐crotubule preparations. Both antibodies bind to the 200‐ki‐lodalton (kd) (NF‐H) and 160‐kd (NF‐M) but not to the 68‐kd (NF‐L) NF triplet proteins. They also bind to high‐molecular‐weight microtubule‐associated proteins (MAPs) and t. AD10 immunostains MAP2 and MAP1 families, whereas AB18 stains mainly MAP1 bands. Preincubation of intact filament preparation or nitrocellulose strips containing elec‐troblotted NF proteins with Escherichia coli alkaline phos‐phatase completely blocks AD 10 binding and partially blocks binding of AB18. These results suggest that the determinants recognized by these antibodies are phosphorylated. Immunoblotting of peptide fragments generated by limited proteolysis of NF proteins with α‐chymotrypsin and Staphylococcus aureus V8 protease shows that the localization of the antigenic determinants to AD 10 and AB18 in NF‐H is ∼ 100 and 60 kd, respectively, away from the carboxy terminal, a region previously shown to form the NF projection side arm. In NF‐M, the antigenic determinants to both antibodies are located also in the projection side arm, in a 60‐kd polypeptide adjacent to the α‐helical filament core. The results show that ANTs contain at least two phosphorylated antigenic sites that are present in NF and MAPs, a finding suggesting that ANTs may be composed of proteins or their fragments with epitopes shared by cytoskeletal proteins.