Distinct macrophage subpopulations regulate viral encephalitis but not viral clearance in the CNS

Area of Science:

• Neuroimmunology
• Virology
• Immunology

Background:

• Intranasal vesicular stomatitis virus (VSV) infection causes acute encephalitis with significant myeloid and T cell infiltration in the brain.
• Phagocytic cells, such as macrophages and dendritic cells, play crucial roles in immune responses, including those against viral infections in the central nervous system (CNS).

Purpose of the Study:

• To investigate the specific roles of distinct phagocytic cell populations in the pathogenesis of VSV-induced encephalitis.
• To determine whether peripheral macrophages, splenic marginal zone dendritic cells, or brain perivascular macrophages differentially regulate VSV encephalitis and viral clearance.

Main Methods:

• Utilized genetic models to ablate peripheral macrophages.
• Employed depletion strategies for splenic marginal zone dendritic cells and brain perivascular macrophages.
• Assessed VSV encephalitis severity, morbidity, mortality, and viral load in the CNS following intranasal VSV challenge.

Main Results:

• Ablation of peripheral macrophages did not affect VSV encephalitis or viral clearance from the brain.
• Depletion of splenic marginal zone dendritic cells exacerbated VSV encephalitis, increasing morbidity and mortality.
• Selective depletion of brain perivascular macrophages suppressed VSV encephalitis but did not alter viral clearance.

Conclusions:

• Two distinct phagocytic populations, splenic marginal zone dendritic cells and brain perivascular macrophages, regulate VSV encephalitis in a non-redundant manner.
• Neither of these phagocytic populations is essential for viral clearance within the CNS during VSV encephalitis.
• These findings highlight the specific immunoregulatory roles of distinct phagocytic subsets in neuroinflammation.