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Hematogenous origin of the inflammatory response in acute poliomyelitis
Abstract:
To determine the origin of the inflammatory response, and in particular the microglial rod cell response, in acute viral encephalitis, 4-week-old Swiss mice were injected with tritiated thymidine to label actively dividing cells prior to infection with the Lansing type 2 strain of poliovirus. As expected, the majority of polymorphonuclear and mononuclear leukocytes within the central nervous system perivascular infiltrates were shown to be hematogenous in origin. As early as 24 hours after infection, isotope-labeled cells having light histological and ultrastructural features consistent with microglia and microglial rod cells were identified within brain parenchyma and were shown to participate in neuronophagia and formation of glial nodules. Supraependymal and suprachoroidal cells were also shown to contain the label. However, neither endothelial cells nor pericytes contained label as determined by electron microscopy. These studies support a hematogenous origin for all cellular elements of the classic inflammatory response in viral infections of brain.
Insights
This study investigated the origin of inflammatory cells in viral encephalitis. Results show that microglia and other inflammatory cells in the brain originate from the blood, challenging previous assumptions.
Area of Science:
- Neuroscience
- Immunology
- Virology
Background:
- Acute viral encephalitis triggers an inflammatory response within the central nervous system (CNS).
- The origin of microglial rod cells, a key component of this response, has been debated.
Purpose of the Study:
- To determine the origin of inflammatory cells, specifically microglial rod cells, during acute viral encephalitis.
Main Methods:
- Swiss mice were injected with tritiated thymidine to label dividing cells before poliovirus infection.
- Histological and ultrastructural analyses were used to identify labeled cells within the CNS.
Main Results:
- Hematogenous (blood-borne) origin was confirmed for polymorphonuclear and mononuclear leukocytes in CNS perivascular infiltrates.
- Isotope-labeled cells consistent with microglia and microglial rod cells were found in the brain parenchyma, participating in neuronophagia and glial nodule formation.
- Supraependymal and suprachoroidal cells also contained the label; endothelial cells and pericytes did not.
Conclusions:
- All cellular elements of the inflammatory response in viral brain infections, including microglia, originate from the blood.
- This finding supports a hematogenous origin for the cellular response in viral encephalitis.