Microglia subtypes in acute, subacute, and chronic multiple sclerosis.

Area of Science:

• Neuroscience
• Immunology
• Pathology

Background:

• Microglia are the resident immune cells of the central nervous system (CNS).
• Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS.
• The origin of myelin phagocytes in MS lesions has been debated, with Pío del Río Hortega proposing microglia as the primary source.

Purpose of the Study:

• To investigate microglia morphology in early and late stages of multiple sclerosis (MS).
• To determine the origin of myelin phagocytes in MS lesions.
• To clarify the role of microglia in the pathogenesis of MS.

Main Methods:

• Immunohistochemical examination of archival paraffin-embedded tissue samples from 25 MS cases.
• Analysis of microglia morphology and interaction with other immune cells.
• Identification of specific cellular markers, including MHC class II and MRP14.

Main Results:

• Myelin phagocytes in MS lesions were found to originate primarily from infiltrating monocytes, not resident microglia.
• "Wall microglia" expressing MHC class II were observed at plaque margins, sometimes associated with astrocytes.
• Microglial nodules formed by interactions between microglia and monocytes were present in chronic MS, and "activated" microglia were prominent in areas without active demyelination.

Conclusions:

• Myelin phagocytes in MS are derived entirely from infiltrating MRP14-positive monocytes.
• Resident microglia, as described by Río Hortega, appear to play an anti-inflammatory role in MS.
• These findings challenge the traditional view of microglia having a destructive role in MS pathogenesis.