A biosafety level-2 mouse model for studying betacoronavirus-induced acute lung damage and systemic manifestations.

The emergence of life-threatening zoonotic diseases caused by betacoronavirus, including the ongoing COVID-19 pandemic, has highlighted the need for developing preclinical models mirroring respiratory and systemic pathophysiological manifestations seen in infected humans. Here, we showed that C57BL/6J wild-type mice intranasally inoculated with the murine betacoronavirus MHV-3 develop a robust inflammatory response leading to acute lung injuries, including alveolar edema, hemorrhage, and fibrin thrombi. Although such histopathological changes seemed to resolve as the infection advanced, they efficiently impaired the respiratory function, as the infected mice displayed restricted lung distention and increased respiratory frequency and ventilation. Following respiratory manifestation, the MHV-3 infection became systemic and a high virus burden could be detected in multiple organs alongside with morphological changes. The systemic manifestation of MHV-3 infection was also marked by a sharp drop in the number of circulating platelets and lymphocytes, besides the augmented concentration of the pro-inflammatory cytokines IL-1β, IL-6, IL-12, IFN-γ, and TNF, thereby mirroring some clinical features observed in moderate and severe cases of COVID-19. Importantly, both respiratory and systemic changes triggered by MHV-3 infection were greatly prevented by blocking TNF signaling, either via genetic or pharmacologic approaches. In line, TNF blockage also diminished the infection-mediated release of pro-inflammatory cytokines and virus replication of human epithelial lung cells infected with SARS-CoV-2. Collectively, results show that MHV-3 respiratory infection leads to a large range of clinical manifestations in mice and may constitute an attractive, lower cost, biosafety level-2 in vivo platform for evaluating the respiratory and multi-organ involvement of betacoronavirus infections. Importance Mouse models have long been used as valuable in vivo platforms to investigate the pathogenesis of viral infections and effective countermeasures. The natural resistance of mice to the novel betacoronavirus SARS-CoV-2, the causative agent of COVID-19, has launched a race towards the characterization of SARS-CoV-2 infection in other animals (e.g. hamsters, cats, ferrets, bats, and monkeys) as well as the adaptation of the mouse model, by either modifying the host or the virus. In the present study, we utilized the natural pathogen of mice MHV as a prototype to model betacoronavirus-induced acute lung injure and multi-organ involvement under biosafety level 2 condition. We showed that C57BL/6J mice intranasally inoculated with MHV-3 develops a severe disease which includes acute lung damage and respiratory distress preceding systemic inflammation and death. Accordingly, the proposed animal model may provide a useful tool for studies regarding betacoronavirus respiratory infection and related diseases.