Glial tau-positive structures lack the sequence encoded by exon 3 of the tau protein gene.

Tau protein comprises six distinct isoforms defined by the presence or absence of sequences encoded by alternatively spliced exon 2, 3 and 10. We have investigated immunohistochemically the expression of exon 3-derived fragment (E-3) of tau protein in brains of patients with Alzheimer's disease (AD) and other neurodegenerative diseases in which the abnormal accumulation of tau protein takes place. In AD, a subset of neurofibrillary tangles, neuropil threads and dystrophic neurites in senile plaques were stained positively with an anti-E-3 antibody. In sharp contrast, glial tau-positive structures, such as astrocytic plaques and oligodendroglial coiled bodies, were negative for E-3 in all cases examined in this study. This is the first report to discriminate tau-positive inclusions in glial cells from those in neurons at the molecular level.