Early events in reovirus infection influence induction of innate immune response

Abstract

Mammalian orthoreovirus (MRV) is a double-stranded (ds)RNA virus which encapsidates its 10 genome segments within a double-layered viral particle. MRV infection triggers an antiviral response in host cells which serves to limit viral replication. This antiviral response is initiated by recognition of the incoming viral genome by host sensors present in the cytoplasm. However, how host sensors gain access to the MRV genome is unclear as this dsRNA is protected by the viral particle proteins throughout infection. To initiate infection, MRV particles are endocytosed and the outer viral particle layer is disassembled through the action of host proteases. This disassembly event is required for viral escape into the cytoplasm to begin replication. We show that endosomal proteases are required even late in infection, when disassembly is complete, to induce an immune response to MRV. Additionally, counter to dogma, our data demonstrate at least some viral dsRNA genome is exposed and detectable during entry. We hypothesize that some proportion of MRV particles remain trapped within endosomes, allowing for the breakdown of these particles and release of their genome. We show that rapidly uncoating mutants escape the endosome more rapidly and induce a diminished immune response. Further, we show that particles entering through dynamin-independent pathways evade detection by host sensors. Overall, our data provide new insight into how genomes from entering reovirus particles are detected by host cells.

The reovirus σ1 attachment protein influences the stability of its entry intermediate

“…Thus, it appears that a lower 1 level may be advantageous at least in the environment of cultured cells to allow the virus to launch infection prior to when host responses kick in. We have also recently shown that viruses that undergo ISVP-to-ISVP* more readily elicit a lower innate immune response (59). Thus, particles with fewer 1 or those with suboptimal 1-λ2 interactions that promote ISVP* formation could limit the activation of the innate immune response and be beneficial to the virus.…”