ApoE immunoreactivity and microglial cells in Alzheimer's disease brain.

The spatial relationship of apolipoprotein E (apoE)-like immunoreactivity (IR) to amyloid beta-peptide (A beta), astrocytes and microglial cells in the brain of Alzheimer's disease was studied by double immunolabelling. Diffuse apoE-like IR was seen in A beta diffuse deposits, and markedly increased in the core of classic senile plaques. Microglial cells, sometimes immunoreactive for apoE, were frequent in areas of apoE-like IR, where they often grouped into clusters in the core of apoE-labelled senile plaques. Although astrocytic processes were seen within these senile plaques, the cell bodies were always at a distance from the core. None of these astrocytes expressed apoE-like IR. Microglial cells, some of them immunoreactive for apoE, were seen in the center of apoE-labelled senile plaques. These data suggest that microglial cells play a more significant role than astrocytes in apoE deposition in senile plaques of Alzheimer disease.