Adaptive Immunity Restricts Replication of Novel Murine Astroviruses

Abstract

The mechanisms of astrovirus pathogenesis are largely unknown, in part due to a lack of a small-animal model of disease. Using shotgun sequencing and a custom analysis pipeline, we identified two novel astroviruses capable of infecting research mice, murine astrovirus (MuAstV) STL1 and STL2. Subsequent analysis revealed the presence of at least two additional viruses (MuAstV STL3 and STL4), suggestive of a diverse population of murine astroviruses in research mice. Complete genomic characterization and subsequent phylogenetic analysis showed that MuAstV STL1 to STL4 are members of the mamastrovirus genus and are likely members of a new mamastrovirus genogroup. Using Rag1 ؊/؊ mice deficient in B and T cells, we demonstrate that adaptive immunity is required to control MuAstV infection. Furthermore, using Stat1 ؊/؊ mice deficient in innate signaling, we demonstrate a role for the innate immune response in the control of MuAstV replication. Our results demonstrate that MuAstV STL permits the study of the mechanisms of astrovirus infection and host-pathogen interactions in a genetically manipulable smallanimal model. Finally, we detected MuAstV in commercially available mice, suggesting that these viruses may be present in academic and commercial research mouse facilities, with possible implications for interpretation of data generated in current mouse models of disease.

Type I Interferon Response Limits Astrovirus Replication and Protects against Increased Barrier Permeability In Vitro and In Vivo

“…Sequence analysis on ϳ500 nucleotides of the ORF2 revealed that our colonies are infected with an MuAstV genotype most similar to STL4 (Fig. 5A) (23). The capsid is 99% similar to STL4 at the nucleotide level and 98% similar via amino acid.…”

“…All of the mice in our IFNaR Ϫ/Ϫ colony are MuAstV positive. This may have occurred through contact with infected animals or bedding, given that cohousing can lead to infection (23), as can exposure to contaminated bedding (B. Sharp et al, unpublished data).…”

“…Mouse colonies at St. Jude Children's Research Hospital were screened for the presence of murine astrovirus (MuAstV) by realtime reverse transcription-PCR (RT-PCR) as described previously (23). We identified several immunocompromised colonies persistently infected with MuAstV, including our IFNaR Ϫ/Ϫ (IFNaR stands for alpha interferon receptor) mice.…”

“…Finally, to determine the importance of type 1 IFNs in astrovirus infection in vivo, we developed a novel murine astrovirus (MuAstV) model based on our and other groups' findings that many laboratory mice are endogenously infected with MuAstV (23,44). To do this, we screened our St. Jude colonies for MuAstV by real-time PCR and found that numerous immunocompromised strains including CD1, RAG, and type 1 IFN-␣ receptor (IFNaR) knockout mice (as examples) were persistently shedding MuAstV.…”

“…Briefly, for 12 tubes, 250 l of feces was suspended in 0.5 ml PBS in each tube, homogenized using 2-mm zirconium oxide beads (Next Advance) beads for 4 min on speed setting 4 (Next Advance air cooling bullet blender), and pelleted by centrifugation at 12,000 rpm for 5 min. The supernatants were pooled and filtered through a 0.2-m filter (fecal filtrate) and viral copy number quantified by realtime RT-PCR (23). Briefly, viral RNA was isolated from feces by the QIAamp viral RNA minikit (Qiagen) according to the manufacturer's instructions.…”