Immunohistochemical evidence for the lack of amyloid P component in some intracerebral amyloids.

Sections of brain tissue from patients with Alzheimer's disease with amyloid deposits in vessels, in plaques, and within nerve cells were studied by means of an immunoperoxidase method using a specific antiamyloid P component (AP) antiserum. Amyloid deposits in vessels were found to be strongly positive for protein AP, whereas the Alzheimer's plaques and the neurofibrillary tangles were negative or only weakly positive. The absence of protein AP in some intracerebral amyloid deposits might be due to an inability of the protein AP in some intracerebral amyloid deposits might be due to an inability of the protein to penetrate the blood-brain barrier. These findings support the theory that protein AP is absorbed to already formed amyloid fibrils, but the possibility that it may participate in the formation of vascular amyloid cannot be dismissed. The findings also indicate that protein AP is not necessary for the formation of amyloid fibrils at least in some forms of cerebral amyloidosis.