The macrophage in MS: just a scavenger after all? Pathology and pathogenesis of the acute MS lesion

Area of Science:

• Neuropathology
• Neuroimmunology
• Demyelinating Diseases

Background:

• Multiple sclerosis (MS) neuropathology research focuses on active lesions with macrophage activity and demyelinated axons.
• The prevailing hypothesis suggests a T-cell dependent, macrophage-mediated autoimmune attack on myelin initiates MS.
• This autoimmune hypothesis, supported by animal models like experimental allergic encephalomyelitis, is now being re-examined.

Purpose of the Study:

• To analyze pathological events preceding myelin phagocytosis in nascent multiple sclerosis lesions.
• To investigate the initiating events in the evolution of MS lesions.
• To explore alternative mechanisms driving MS pathogenesis.

Main Methods:

• Analysis of pathological events in evolving multiple sclerosis lesions shortly after relapse onset.
• Examination of prephagocytic changes in nascent MS lesions.
• Comparative pathology of lesions in patients with varying pathological changes.

Main Results:

• Prephagocytic changes in evolving lesions suggest oligodendrocyte cell death initiates local macrophage scavenger activity.
• This initiates an inflammatory response, potentially amplifying lesion development.
• Pathological heterogeneity in MS appears to stem from the evolution of lesional pathology.

Conclusions:

• The study challenges the traditional autoimmune attack model for multiple sclerosis.
• Oligodendrocyte cell death and myelin sheath changes may be early triggers for macrophage activity.
• Lesion evolution, rather than pathogenic heterogeneity, likely accounts for the diverse pathological presentations in MS.