Introduction: The SARS CoV2 pandemic has produced morbidity and mortality worldwide depending on age, body mass index, cardiovascular disease and other factors. Of the human CoVs, SARS-CoV2 and HCoV-NL63 bind ACE2. HCoV-NL63 causes upper respiratory tract infections in children, pneumonia in the elderly, and even Kawasaki disease in children. Hypothesis: HCoV-NL63 produces lung inflammation in mice expressing the human ACE2 protein. Methods: HCoV-NL63 (ATCC) was propagated in Caco-2 cells. Virus cytopathic effect in Vero cells at 48 h infection was determined by TCID 50 . B6.Cg-Tg(K18-ACE2)2Prlmn mice (JAX Labs) express the human ACE2 protein in epithelial cells using the keratin 18 promoter. Eight-10 week-old K18-hACE2 or C57BL6/J mice were infected with 50 µL (100,000 TCID 50 ) HCoV-NL63 or sham intranasally and euthanized at 2, 4, and 7 days post-treatment. Mouse lungs were assessed for histology, IFN and cytokine mRNAs, ACE2, viral RNA and HCoV-NL63 proteins (nucleoprotein, Nsp3 and Nsp4). Primers from the HCoV-NL63 sequence (NC_005831.2) were used to measure vRNA by qPCR. Polyclonal antibodies to Nsp3 and 4 were (Chen et al, J Virol 2007) used with antibodies to human ACE2 (InVitrogen), HCoV-NL63 nucleoprotein (clone 2D5, Eurofins) for immunohistochemistry. Results:HCoV-NL63 cytopathic effects in Vero cells colocalized with viral nucleoprotein. Virus propagated in K18-hACE2 but not C57BL6/J mice. vRNA levels plateaued 4 days after infection and were detectable 7 days after infection. Lung mRNA expression of IFN-α, IFN-β, IFN-λ, CXCL1 and IL-6 were significantly increased 48 h after infection in HCoV-NL63-treated K18-hACE2 but not C57BL6/J mice (N=3, p<0.05, Kruskal-Wallis test). Mouse lung had bronchovascular and peribronchial inflammation evident 7 days after infection. Nucleoprotein was found on the apical surface of airway epithelial cells of HCoV-NL63-but not shaminfected K18-hACE2 mice, and Nsp3 and Nsp4 were found in the basal cytoplasm of airway epithelial cells. Conclusion: Human coronavirus NL63 infects K18-ACE2 mice with an airway inflammatory response. Viral replication is evident. This model may be used to study HCoV-NL63-induced exacerbation of allergic airways disease; the effect of allergy, obesity and aging on human coronavirus infection, and possible crossimmunity between HCoV-NL63 and other respiratory viruses
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