Immunocytochemical study of alpha 1-antichymotrypsin in the senescent cerebral amyloid.

We immunocytochemically examined the brains of patients with dementia of the Alzheimer type (DAT), to clarify the relation between alpha 1-antichymotrypsin and cerebral amyloid. Antiserum to synthetic beta protein (1-28 residue) was used to stain the senile plaque amyloid and cerebrovascular amyloid. Cryostat sections and paraffin embedded sections pretreated with formic acid were prepared for staining beta protein-like immunoreactivity. Fine, amorphous cerebral amyloid deposits were also positive. alpha 1-antichymotrypsin-like immunoreactivity was also found in senile plaques and cerebrovascular amyloid. Primitive plaque, typical plaque, core plaque and amorphous cerebral amyloid deposits had alpha 1-antichymotrypsin-like immunoreactivity. Eosinophilic extracellular tangles were also positive. Hirano bodies were weakly stained. Intracellular tangles and granulovacuolar degeneration were negative. Double immunoenzymatic staining revealed that alpha 1-antichymotrypsin-like immunoreactivity was very closely related to beta protein-positive senile plaques. About 99% of all plaques had both alpha 1-antichymotrypsin- and beta protein-like immunoreactivities. These results indicate that alpha 1-antichymotrypsin is one of the components of the senile plaque amyloid.