Regional Differences in Blood-Brain Barrier Permeability Changes and Inflammation in the Apathogenic Clearance of Virus from the Central Nervous System

The loss of blood-brain barrier (BBB) integrity in CNS inflammatory responses triggered by infection and autoimmunity has generally been associated with the development of neurological signs. In the present study, we demonstrate that the clearance of the attenuated rabies virus CVS-F3 from the CNS is an exception; increased BBB permeability and CNS inflammation occurs in the absence of neurological sequelae. We speculate that regionalization of the CNS inflammatory response contributes to its lack of pathogenicity. Despite virus replication and the expression of several chemokines and IL-6 in both regions being similar, the up-regulation of MIP-1β, TNF-α, IFN-γ, and ICAM-1 and the loss of BBB integrity was more extensive in the cerebellum than in the cerebral cortex. The accumulation of CD4- and CD19-positive cells was higher in the cerebellum than the cerebral cortex. Elevated CD19 levels were paralleled by κ-L chain expression levels. The timing of BBB permeability changes, κ-L chain expression in CNS tissues, and Ab production in the periphery suggest that the in situ production of virus-neutralizing Ab may be more important in virus clearance than the infiltration of circulating Ab. The data indicate that, with the possible exception of CD8 T cells, the effectors of rabies virus clearance are more commonly targeted to the cerebellum. This is likely the result of differences in the capacity of the tissues of the cerebellum and cerebral cortex to mediate the events required for BBB permeability changes and cell invasion during virus infection.