Generation of a monoclonal antibody to the carboxy-terminal domain of tau by immunization with the amino-terminal domain of the amyloid precursor protein.

A fusion protein between beta-galactosidase and the amino-terminal domain of amyloid precursor protein (APP) was used as an immunogen for the production of monoclonal antibodies. One of these antibodies, the 5D12 monoclonal antibody, labeled the neurofibrillary tangles (NFT) by immunohistochemistry, as well as isolated paired helical filaments (PHF) in electron microscopy. In immunoassay, the ascitic fluid produced by the 5D12 clone was demonstrated to contain a high titer of antibodies to heat-stable microtubule associated proteins (MAPs). By immunoblotting, the proteins recognized in heat-stable MAPs were found to correspond to tau proteins. The 5D12 antibody recognized normal tau isolated from rat and human brain homogenates, and PHF-tau isolated from the brain of patients with Alzheimer's disease (AD). By immunoblotting, the 5D12 antibody also recognized the full-length recombinant tau protein but not the fusion protein used as an immunogen. The immunoreactivity of the 5D12 antibody with tau was completely abolished when the half-carboxy domain of tau, containing the tubulin-binding repeats, was removed. This study demonstrates that the use of the amino-terminal domain of APP as an immunogen led to the generation of a monoclonal antibody to the half-carboxy domain of tau.