Hematogenous origin of the inflammatory response in acute poliomyelitis.

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.