Role of microglia in plaque formation in senile dementia of the Alzheimer type. An immunohistochemical study.

Using immunohistochemical and enzyme histochemical methods, we have investigated the presence of mononuclear phagocytic cells around senile plaques in six brains from patients with senile dementia of the Alzheimer type (SDAT). It is generally supposed that reactive microglial cells are involved in amyloid formation "as representatives of the reticuloendothelial system in the brain." We used different monoclonal antibodies directed against cells of the mononuclear phagocyte lineage, antibodies against the macrophage markers alpha 1-antichymotrypsin and lysozyme, and the lectin WGA, in addition to enzyme histochemical staining for nonspecific esterase and acid phosphatase. It was concluded that no macrophages of the mononuclear phagocyte lineage are involved in plaque formation. The role of glial cells in amyloid formation is discussed.