Type Ii Interferon Signaling In The Brain During A Viral Infection With Age-Dependent Pathogenesis

Viral infections of the central nervous system (CNS) often cause disease in an age-dependent manner, with greater neuropathology during the fetal and neonatal periods. Transgenic CD46+ mice model these age-dependent outcomes through a measles virus infection of CNS neurons. Adult CD46+ mice control viral spread and survive the infection in an interferon gamma (IFN gamma)-dependent manner, whereas neonatal CD46+ mice succumb despite similar IFN gamma expression in the brain. Thus, we hypothesized that IFN gamma signaling in the adult brain may be more robust, potentially due to greater basal expression of IFN gamma signaling proteins. To test this hypothesis, we evaluated the expression of canonical IFN gamma signaling proteins in the neonatal and adult brain, including the IFN gamma receptor, Janus kinase (JAK) 1/2, and signal transducer and activator of transcription-1 (STAT1) in the absence of infection. We also analyzed the expression and activation of STAT1 and IFN gamma-stimulated genes during MV infection. We found that neonatal brains have equivalent or greater JAK/STAT1 expression in the hippocampus and the cerebellum than adults. IFN gamma receptor expression varied by cell type in the brain but was widely expressed on neuronal and glial cells. During MV infection, increased STAT1 expression and activation correlated with viral load in the hippocampus regardless of age, but not in the cerebellum where viral load was consistently undetectable in adults. These results suggest the neonatal brain is capable of initiating IFN gamma signaling during a viral infection, but that downstream STAT1 activation is insufficient to limit viral spread.