Microglial cell depletion is fatal with low level picornavirus infection of the central nervous system.

Microglia are the only resident myeloid cell in the central nervous system (CNS) parenchyma, but the role of microglia in the context of neurotropic viral infection is poorly understood. Using different amounts of Theiler's murine encephalomyelitis virus (TMEV) in a preclinical model of epilepsy and PLX5622, a colony stimulating factor-1 receptor inhibitor that selectively depletes microglia in the CNS, we report that microglia-depleted, TMEV-infected mice develop seizures, manifest paralysis, and uniformly succumb to fatal encephalitis regardless of viral amount. CNS demyelination correlates with viral amount; however, viral amount does not correlate with axon damage and TMEV antigen in the CNS.