Complement C3 on microglial clusters in multiple sclerosis occur in chronic but not acute disease: Implication for...

Area of Science:

• Neuroscience
• Immunology
• Pathology

Background:

• Microglial clusters with C3d deposits are found in multiple sclerosis (MS) lesions.
• These clusters were hypothesized to represent early stages of MS lesion formation.
• Previous studies have not confirmed their presence in acute MS cases.

Purpose of the Study:

• To investigate the presence and role of C3d+ microglial clusters in acute and chronic MS.
• To determine if these clusters are specific to MS or also occur in other neurological conditions.
• To elucidate the potential contribution of C3d+ microglial clusters to MS pathogenesis.

Main Methods:

• Analysis of postmortem brain tissue from acute and chronic MS patients.
• Examination of brain tissue from ischemic stroke and experimental traumatic brain injury (TBI) cases.
• Immunohistochemical staining for C3d, microglial markers, and axonal transport indicators.

Main Results:

• C3d+ microglial clusters were identified in chronic MS, but not in acute MS.
• These clusters were associated with slowly expanding lesions and impaired axonal transport.
• C3d+ microglial clusters were also observed in stroke and TBI, indicating a lack of MS specificity.
• No association with antibody deposits or terminal complement activation was found.

Conclusions:

• C3d+ microglial clusters are not indicative of an acute attack on myelinated axons in MS.
• These clusters are unlikely to drive new lesion formation in MS.
• They may represent a mechanism for clearing irreversibly damaged axons in chronic neurodegenerative conditions.