title: N1L is an ectromelia virus virulence factor and essential for in vivo spread upon respiratory infection.
abstract: The emergence of zoonotic orthopoxvirus infections and the threat of possible intentional release of pathogenic orthopoxviruses have stimulated renewed interest in understanding orthopoxvirus infections and the resulting diseases. Ectromelia virus (ECTV), the causative agent of mousepox, offers an excellent model system to study an orthopoxvirus infection in its natural host. Here, we investigated the role of the vaccinia virus ortholog N1L in ECTV infection. Respiratory infection of mice with an N1L deletion mutant virus (ECTVΔN1L) demonstrated profound attenuation of the mutant virus, confirming N1 as an orthopoxvirus virulence factor. Upon analysis of virus dissemination in vivo, we observed a striking deficiency of ECTVΔN1L spreading from the lungs to the livers or spleens of infected mice. Investigating the immunological mechanism controlling ECTVΔN1L infection, we found the attenuated phenotype to be unaltered in mice deficient in Toll-like receptor (TLR) or RIG-I-like RNA helicase (RLH) signaling as well as in those missing the type I interferon receptor or lacking B cells. However, in RAG-1(-/-) mice lacking mature B and T cells, ECTVΔN1L regained virulence, as shown by increasing morbidity and virus spread to the liver and spleen. Moreover, T cell depletion experiments revealed that ECTVΔN1L attenuation was reversed only by removing both CD4(+) and CD8(+) T cells, so the presence of either cell subset was still sufficient to control the infection. Thus, the orthopoxvirus virulence factor N1 may allow efficient ECTV infection in mice by interfering with host T cell function.
authors.affiliation: Paul-Ehrlich-Institut, Langen, Germany.
authors.forename: Meike S
authors.initials: MS
authors.lastname: Gratz
authors.forename: Yasemin
authors.initials: Y
authors.lastname: Suezer
authors.forename: Melanie
authors.initials: M
authors.lastname: Kremer
authors.forename: Asisa
authors.initials: A
authors.lastname: Volz
authors.forename: Monir
authors.initials: M
authors.lastname: Majzoub
authors.forename: Kay-Martin
authors.initials: KM
authors.lastname: Hanschmann
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kalinke
authors.forename: Astrid
authors.initials: A
authors.lastname: Schwantes
authors.forename: Gerd
authors.initials: G
authors.lastname: Sutter
mesh_terms: D000818:Animals; D001835:Body Weight; D004481:Ectromelia virus / Q000472:pathogenicity*; D004482:Ectromelia, Infectious / Q000473:pathology* / Q000821:virology*; D005260:Female; D017353:Gene Deletion; D006651:Histocytochemistry; D007108:Immune Tolerance; D008099:Liver / Q000473:pathology / Q000821:virology; D008168:Lung / Q000473:pathology / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D012141:Respiratory Tract Infections / Q000473:pathology* / Q000821:virology*; D013154:Spleen / Q000821:virology; D016019:Survival Analysis; D013601:T-Lymphocytes / Q000276:immunology; D019562:Viral Load; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D014764:Viral Proteins; D037521:Virulence Factors