IMMUNOREACTIVITY OF AN ANTIBODY TO A BETA A4 SEQUENCE WITH ALZHEIMER PAIRED HELICAL FILAMENTS AND TAU-PROTEIN/

Beta/A4, a peptide that forms the extracellular amyloid fibrils of Alz heimer senile plaques, has also been proposed to be a component of Alz heimer paired helical filaments (PHFs). We compared BR88, an antiserum to amino acids 1-12 of beta/A4, with BR126, an antiserum to the, sequ ence SEKLDFKDRVQS in tau protein, since tau protein is the only confir med component of PHFs. In enzyme-linked immunosorbent assays (ELISAs), both antibodies reacted with pronase-treated PHFs better after PHFs w ere treated with guanidine. Tau protein shares no sequence homology wi th beta/A4. Nevertheless, BR88 cross-reacted with human recombinant ta u isoforms by ELISA and Western blot analysis with potencies comparabl e to those for anti-tau antibodies. BR88 reacted with a beta/A4 peptid e as well on a molar basis as with tau protein and showed some reactiv ity to the tubulin-binding region of tau protein. In conclusion, the b eta/A4 antiserum BR88 cross-reacts with tau protein, possibly explaini ng its reactivity with PHFs.