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Continual breakdown and regeneration of myelin in progressive multiple sclerosis plaques
Abstract:
Plaques with lipid macrophages and macrophages containing undigested myelin fragments from five multiple sclerosis patients were studied by light microscopy of epoxy-embedded tissue (five cases) and electron microscopy (one case). Cell counts determined electron microscopically revealed that oligodendrocytes were reduced in number in areas of commencing myelin breakdown. The major mechanism of myelin destruction was phagocytosis by macrophages of intact myelin sheaths in the presence of very small numbers of lymphocytes and plasma cells. When plaques were orientated to allow examination of whole myelin internodes, it was found that most lesions, including lesions known to have been present for less than ten months, contained remyelinating internodes, sometimes in numbers large enough to form shadow plaques. It is concluded that the two processes of sometimes massive remyelination and active demyelination frequently coexist in "fatty" subacute plaques filled with lipid-containing macrophages, and that myelin breakdown at the edges of progressive lesions includes destruction of remyelinating internodes.
Insights
Multiple sclerosis plaques show active myelin destruction and simultaneous remyelination. Macrophages engulf myelin, while oligodendrocytes decrease, indicating complex lesion dynamics.
Area of Science:
- Neuroscience
- Pathology
- Immunology
Background:
- Multiple sclerosis (MS) is characterized by demyelination and neuroinflammation.
- Understanding the cellular mechanisms of myelin damage and repair in MS is crucial for developing effective therapies.
Purpose of the Study:
- To investigate the cellular processes involved in myelin breakdown and remyelination in active multiple sclerosis plaques.
- To identify the primary mechanisms of myelin destruction and the role of different cell types in lesion formation.
Main Methods:
- Light microscopy of epoxy-embedded tissue from five MS patients.
- Electron microscopy of one MS patient's plaque tissue.
- Cell counting to quantify oligodendrocyte numbers in demyelinating areas.
Main Results:
- Oligodendrocytes were reduced in areas of early myelin breakdown.
- Myelin destruction was primarily mediated by macrophages phagocytosing intact myelin sheaths.
- Lymphocytes and plasma cells were present in small numbers.
- Remyelinating internodes were observed in most lesions, including those present for less than ten months, sometimes forming shadow plaques.
Conclusions:
- Active demyelination and significant remyelination frequently coexist in active, lipid-laden MS plaques.
- Myelin breakdown at the edges of progressive lesions can also destroy newly formed remyelinated internodes.
- These findings highlight the dynamic and complex nature of lesion development in multiple sclerosis.