LOCALIZATION OF AMYLOID-P COMPONENT IN HUMAN BRAIN - VASCULAR STAINING PATTERNS AND ASSOCIATION WITH ALZHEIMERS-DISEASE LESIONS

Amyloid P component is a normal serum protein that is highly conserved across phylogeny. Although it resembles the classic acute-phase react ant C-reactive protein, and is considered to be a normal extracellular matrix component, its physiologic role in humans is unknown. Amyloid P component is also colocalized with accumulations of all recognized f orms of amyloid. The present study uses light and electron microscopy to compare the cerebral localization of amyloid P component in cases w ith (n=19) and without (n=15) Alzheimer's disease (AD). In non-AD case s, amyloid P component was predominantly localized to the cerebrovascu lature. Perivascular staining was observed in most cases, more so in t he white than in the gray matter. In AD cases, amyloid P component was localized to all three characteristic histopathologic lesions, namely , neurofibrillary tangles, senile plaques, and amyloid angiopathy. Fur thermore, in cases with prominent staining of gray matter parenchymal lesions, intravascular staining was decreased. Given the fixation and processing methods used, amyloid P component was never seen to be loca lized to the cerebrovascular basement membrane. These data argue again st amyloid P component's postulated role as the anchor for vascular P- amyloid deposition. Because there is no evidence for intrinsic amyloid P component production in brain, its perivascular and parenchymal dis tributions suggest either compromise of the blood-brain barrier or tra nsport across vascular endothelium. (C) 1995 Wiley-Liss, Inc.