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Neurobiol Aging. 2001 May-Jun;22(3):427-34.

3D-Reconstruction of microglia and amyloid in APP23 transgenic mice: no evidence of intracellular amyloid.

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Department of Neuropathology, Institute of Pathology, University of Basel, Basel, Switzerland.


Microglia cells are closely associated with compact amyloid plaques in Alzheimer's disease (AD) brains. Although activated microglia seem to play a central role in the pathogenesis of AD, mechanisms of microglial activation by beta-amyloid as well as the nature of interaction between amyloid and microglia remain poorly understood. We previously reported a close morphological association between activated microglia and congophilic amyloid plaques in the brains of APP23 transgenic mice at both the light and electron microscopic levels [25]. In the present study, we have further examined the structural relationship between microglia and amyloid deposits by using postembedding immunogold labeling, serial ultrathin sectioning, and 3-dimensional reconstruction. Although bundles of immunogold-labeled amyloid fibrils were completely engulfed by microglial cytoplasm on single sections, serial ultrathin sectioning and three-dimensional reconstruction revealed that these amyloid fibrils are connected to extracellular amyloid deposits. These data demonstrate that extracellular amyloid fibrils form a myriad of finger-like channels with the widely branched microglial cytoplasm. We conclude that in APP23 mice a role of microglia in amyloid phagocytosis and intracellular production of amyloid is unlikely.

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