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Ultrastructural localization of complement membrane attack complex (MAC)-like immunoreactivity in brains of patients
Abstract:
The membrane attack complex (MAC) of complement, also known as C5b-9, was localized in Alzheimer's disease (AD) brain by immunoelectron microscopy using a monoclonal antibody to a neoantigenic epitope of soluble C5b-9 (SC5b-9). Immunopositivity was detected in association with lamellated bodies in the neuronal cytoplasm, lipofuscin granules, lysosomes and neurofibrillary tangles (NFTs). Such intracellular localization of MAC-like immunoreactive (MAC-LI) staining suggests that neurons remove membrane-inserted MAC fragments by endocytosis. These endocytosed membrane fragments then proceed by retrograde transport to the perikaryon for lysosomal degradation. Attachment to the abnormal cytoskeletal proteins found in neurofibrillary tangles also occurs. The results provide further evidence that complement-mediated injury of neurons plays a part in the pathophysiology of AD.
Insights
The membrane attack complex (MAC) was found inside neurons in Alzheimer's disease (AD) brains, suggesting neurons internalize and degrade complement fragments, contributing to AD pathology.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregates.
- The complement system, including the membrane attack complex (MAC), plays a role in immune responses and inflammation.
- Previous studies have implicated complement activation in AD pathogenesis.
Purpose of the Study:
- To investigate the intracellular localization of the membrane attack complex (MAC) in Alzheimer's disease (AD) brains.
- To explore the cellular mechanisms involved in MAC processing within neurons in AD.
- To provide further evidence for the role of complement-mediated neuronal injury in AD.
Main Methods:
- Immunoelectron microscopy was used to detect MAC (C5b-9) in AD brain tissue.
- A monoclonal antibody targeting a neoantigenic epitope of soluble C5b-9 (SC5b-9) was employed.
- Localization of MAC-like immunoreactive (MAC-LI) staining was analyzed within neuronal compartments.
Main Results:
- MAC-like immunoreactivity was detected within neuronal cytoplasm, associated with lamellated bodies, lipofuscin granules, lysosomes, and neurofibrillary tangles (NFTs).
- Intracellular localization suggests neurons internalize membrane-inserted MAC fragments via endocytosis.
- Endocytosed MAC fragments appear to undergo retrograde transport to the perikaryon for lysosomal degradation and may associate with NFTs.
Conclusions:
- Neurons actively internalize and process membrane-inserted MAC fragments in Alzheimer's disease.
- This intracellular processing and potential association with NFTs indicate a role for endocytosis in MAC handling within AD neurons.
- The findings support the hypothesis that complement-mediated neuronal injury contributes to the pathophysiology of Alzheimer's disease.