Differential expression of alpha 1-antichymotrypsin in the aged human brain.

The localization of alpha 1-antichymotrypsin (ACT) mRNA and ACT immunoreactivity (ACT-IR) were examined in 12 brains obtained at post-mortem from elderly patients, four of whom had Alzheimer's disease. A biotinylated oligonucleotide probe was used for in situ hybridization histochemistry and the relationship between the expression of both ACT mRNA and ACT-IR and the extent of beta protein or tau deposition were investigated. The extent of beta-plaques, tau-tangles, and ACT-IR were rated from (-) to (++). In brains without plaques and tangles, there were no detectable ACT mRNA signals in the gray matter, and those in the white matter were weak; in these brains, ACT-IR was generally weak. The brains with beta-plaques but no tangles showed weak ACT mRNA expression in astrocytes of both the gray and white matter; they also showed weak ACT-IR in the astrocytes. In the brains from patients with Alzheimer's disease with both plaques and tangles, ACT mRNA was expressed intensely in a majority of the astrocytes in the white and gray matter. Some senile plaques-associated astrocytes expressed ACT mRNA and ACT-IR was strong in the white matter astrocytes. ACT-IR and ACT mRNA expression in astrocytes was correlated with the extent of beta and tau depositions.