Infection of NOD.SCID.IL2rg−/− Mice with Non‐Mouse‐Adapted Swine‐Origin and Human‐Origin H1 and H3 Influenza A Viruses
Authors: Lorbach Joshua N , Nelson Sarah W , Nolting Jacqueline M , Lauterbach Sarah E , Bowman Andrew S 
Published: June 2021

ObjectiveInfluenza A viruses (IAV) emerging from animal reservoirs pose pandemic influenza threat. Investigation of human population immunity against swine‐origin IAVs identified at the animal‐human interface is critical to understanding the risk associated with these viruses. The ability to use humanized mouse models incorporating natural anti‐IAV immunity could advance current pandemic risk assessment strategies. However, it is widely accepted that IAV infection in mice requires serial passage, though the natural susceptibility of immunodeficient mice is unclear. Further, use of mouse‐adapted IAVs may not accurately reflect antigenic and pathologic features of non‐mouse‐adapted viruses. Our objective was to investigate the susceptibility of the immunodeficient NOD.SCID.IL2rg−/− (NSG) mouse strain to infection with non‐mouse‐adapted human‐ and swine‐origin IAVs. We hypothesized that NSG mice would be naturally susceptible to infection with non‐mouse‐adapted human‐ and swine‐origin hemagglutinin subtype 1 (H1) and H3 IAVs.MethodsPairs of adult NSG mice were intranasally inoculated with one of seven IAVs [swine‐origin (H1 delta1, H1 gamma, H3 human‐like, H3 cluster IV), human seasonal (H1N1, H3N2)] (105–106 TCID50 in 50uL PBS) or sterile PBS. Animals were observed for 96 hours post‐challenge prior to euthanasia and postmortem tissue collection. Lungs were split: viral quantification was performed via endpoint dilution assay, and virus‐associated pathology was assessed via microscopic examination of formalin‐fixed paraffin‐embedded (FFPE) tissues.ResultsInfectious virus was recovered from the lungs of all virus‐challenged NSG mice (n=14). H1 subtype IAVs caused rapid weight loss in challenged mice at 96 hours post‐infection (mean decrease 14.1% body weight) as compared to H3 subtype IAV‐challenge and control mice, which showed no significant weight loss. Microscopic lung lesions included acute airway epithelial degeneration and necrosis, acute peribronchial/bronchiolar inflammation, consolidation, and hemorrhage. Pulmonary lesions and immunohistochemical (IHC) labeling in all H1 IAV‐challenged mice (n=8) were consistent with IAV infection, and lesions were most severe in this group. In contrast, the pulmonary pathology in H3 IAV‐challenged mice ranged from mild to absent.ConclusionsThese findings support the general potential of non‐mouse‐adapted IAV isolates to cause clinical and microscopic disease in NSG mice. While this contradicts the general consensus that IAV is not naturally infectious in mice, there are key differences between H1 and H3 subtype IAVs suggesting HA subtype influences infection. Future challenge studies with additional non‐mouse‐adapted IAVs will help clarify this phenomenon and establish the limitations of their use in humanized mouse models of anti‐IAV immunity.Support or Funding InformationFederal funds from Centers of Excellence for Influenza Research and Surveillance, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contract number HHSN272201400006C were used for this work. Additional support provided by The Ohio State University Graduate School.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.