Microglia Play an Important Role in PRV Infection-Induced Immune Responses of the Central Nervous System

Abstract

Abstract Pseudorabies virus (PRV) can infect multiple hosts and lead to fatal encephalitis. There is a significant increase in the number of microglia in the brain of animals infected with PRV. However, whether and how microglia contribute to central nervous system damage in PRV infection remain unknown. In the present study, we elucidated that PRV infection can cause more severe inflammatory cell infiltration, thicker and more numerous vessel sleeve walls, and more severe inflammatory responses in the brains of natural hosts (pigs) than in those of nonnatural hosts (mice). In a mice infection model, activated microglia restricted viral replication in the early stage of infection. Acute neuroinflammation caused by microglia hyperactivation at late-stage of infection. Furthermore, in vitro experiments revealed that microglia restricted viral replication and decreased viral infectivity. This may be associated with the phagocytic ability of microglia because we observed a significant increase in the expression of the membrane receptor TREM2 in microglia, which is closely related to phagocytosis, we observed that depletion of microglia exacerbated neurological symptoms, blood–brain barrier breakdown, and peripheral lymphocyte infiltration. Taken together, we revealed the dual role of microglia in protecting the host and neurons from PRV infection. IMPORTANCE PRV causes a neuro-virulent disease in natural and unnatural hosts which is often fatal. Microglial activation plays an important role in neuroinflammatory diseases. However, how microglia play a role in this process remains unclear. In this study, the differences of pathological changes between pigs and mice infected with PRV were compared. In a mice infection model, activated microglia restricted viral replication in the early stage of infection. Acute neuroinflammation caused by microglia hyperactivation at late-stage of infection. In vitro experiments revealed that microglia restricted viral replication and decreased viral infectivity. New therapeutics targeting microglia activation may help to treat PRV-associated neurocognitive disorders.