Type I interferon signaling limits reoviral tropism within the brain and prevents lethal systemic infection

Abstract

In vivo and ex vivo models of reoviral encephalitis were utilized to delineate the contribution of type I interferon (IFN) to the host’s defense against local central nervous system (CNS) viral infection and systemic viral spread. Following intracranial (i.c.) inoculation with either serotype 3 (T3) or serotype 1 (T1) reovirus, increased expression of IFN-α, IFN-β, and myxovirus-resistance protein (Mx1; a prototypical IFN stimulated gene) was observed in mouse brain tissue. Type I IFN receptor deficient mice (IFNAR−/−) had accelerated lethality, compared to wildtype (B6wt) controls, following i.c. T1 or T3 challenge. Although viral titers in the brain and eyes of reovirus infected IFNAR−/− mice were significantly increased, these mice did not develop neurologic signs or brain injury. In contrast, increased reovirus titers in peripheral tissues (liver, spleen, kidney, heart, and blood) of IFNAR−/− mice were associated with severe intestinal and liver injury. These results suggest that reovirus-infected IFNAR−/− mice succumb to peripheral disease rather than encephalitis per se. To investigate the potential role of type I IFN in brain tissue, brain slice cultures (BSCs) were prepared from IFNAR−/− mice and B6wt controls for ex vivo T3 reovirus infection. Compared to B6wt controls, reoviral replication and virus-induced apoptosis were enhanced in IFNAR−/− BSCs indicating that a type I IFN response, initiated by resident CNS cells, mediates innate viral immunity within the brain. T3 reovirus tropism was extended in IFNAR−/− brains to include dentate neurons, ependymal cells, and meningeal cells indicating that reovirus tropism within the CNS is dependent upon type I interferon signaling.