Increased senile plaques without microglia in Alzheimer's disease

To clarify the association of microglia with senile plaques, the brains from 13 patients with Alzheimer's disease (AD) and 23 nondemented aged controls were investigated immunohistochemically by a double-labeling method using anti-beta-protein antiserum and anti-ferritin antibody, which is a recently reported microglia marker. In addition, a quantitative analysis was performed. The senile plaques which appeared initially in the nondemented aged controls consisted of a diffuse type without any amyloid cores and these were found in the group aged 50-59 years. The great majority of them were found to contain no ferritin-positive microglia. The number and proportion (percentage) of microglia-containing diffuse plaques increased with age. Classical and compact plaques began to appear in the brains of the group aged 70 years and over, and practically all of them contained microglia. These results suggest that microglia are not associated with initial plaque formation, but correlate with amyloid core formation. In AD, the most prominent feature was that the diffuse plaques, which contained either no or only a few ferritin-positive microglia, increased markedly.