Pathogenic human coronaviruses such as the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV) cause acute respiratory illness. Epidemiological data from the 2002-2003 SARS epidemic and recent MERS indicate that there may be sex-dependent differences in disease outcomes. To investigate these differences, we infected male and female mice of different age groups with SARS-CoV and analyzed their susceptibility to the infection. Our results showed that male mice were more susceptible to SARS-CoV infection compared to age matched females. The degree of sex-bias to SARS-CoV infection increased with advancing age such that middle-aged mice showed much more pronounced differences compared to young mice. Enhanced susceptibility of male mice to SARS-CoV was associated with elevated virus titers, enhanced vascular leakage and alveolar edema. These changes were accompanied by increased accumulation of inflammatory monocyte macrophages (IMMs) and neutrophils in the lungs of male mice and depletion of IMMs partially protected these mice from lethal SARS. Moreover, the sex-specific differences were independent of T and B cell responses. Furthermore, ovariectomy or treating female mice with an estrogen receptor antagonist increased mortality indicating a protective effect for estrogen receptor signaling in mice infected with SARS-CoV. Together, these data suggest that sex differences in susceptibility to SARS-CoV in mice parallel those observed in patients and also identify estrogen receptor signaling as critical for protection in females.

In this era of continued emergence of zoonotic virus infections, the rapid development of rodent models represents a critical barrier to public health preparedness, including the testing of antivirus therapy and vaccines. The Middle East respiratory syndrome coronavirus (MERS-CoV) was recently identified as the causative agent of a severe pneumonia. Given the ability of coronavirus to rapidly adapt to new hosts, a major public health concern is that MERS-CoV will further adapt to replication in humans, triggering a pandemic. No small-animal model for this infection is currently available, but studies suggest that virus entry factors can confer virus susceptibility. Here, we show that mice were sensitized to MERS-CoV infection by prior transduction with adenoviral vectors expressing the human host-cell receptor dipeptidyl peptidase 4. Mice developed a pneumonia characterized by extensive inflammatorycell infiltration with virus clearance occurring 6-8 d after infection. Clinical disease and histopathological changes were more severe in the absence of type-I IFN signaling whereas the T-cell response was required for virus clearance. Using these mice, we demonstrated the efficacy of a therapeutic intervention (poly I:C) and a potential vaccine [Venezuelan equine encephalitis replicon particles expressing MERS-CoV spike protein]. We also found little protective cross-reactivity between MERS-CoV and the severe acute respiratory syndrome-CoV. Our results demonstrate that this system will be useful for MERS-CoV studies and for the rapid development of relevant animal models for emerging respiratory viral infections.emerging pathogen | interferon | SARS

SUMMARY Two zoonotic coronaviruses (CoV), SARS-CoV and MERS-CoV have crossed species to cause severe human respiratory disease. Here, we showed that induction of airway memory CD4+ T cells specific for a conserved epitope shared by SARS-CoV and MERS-CoV is a potential strategy for developing pan-coronavirus vaccines. Airway memory CD4+ T cells differed phenotypically and functionally from lung-derived cells and were crucial for protection against both CoVs in mice. Protection was interferon-γ-dependent and required early induction of robust innate and virus-specific CD8+ T cell responses. The conserved epitope was also recognized in SARS-CoV and MERS-CoV-infected human leukocyte antigen DR2 and DR3 transgenic mice, indicating potential relevance in human populations. Additionally, this epitope was cross-protective between human and bat CoVs, the progenitors for many human CoVs. Vaccine strategies that induce airway memory CD4+ T cells targeting conserved epitopes may have broad applicability in the context of new CoV and other respiratory virus outbreaks.

Severe acute respiratory syndrome coronavirus (SARS-CoV IMPORTANCEVirus-specific CD8 T cells are required for pathogen clearance following primary SARS-CoV infection. However, the role of SARS-CoV-specific memory CD8 T cells in mediating protection after SARS-CoV challenge has not been previously investigated. In this study, using a prime-boost immunization approach, we showed that virus-specific CD8 T cells protect susceptible 8-to 10-month-old mice from lethal SARS-CoV challenge. Thus, future vaccines against emerging coronaviruses should emphasize the generation of a memory CD8 T cell response for optimal protection.

bSevere acute respiratory syndrome coronavirus (SARS-CoV) is the etiological agent of a respiratory disease that has a 10% mortality rate. We previously showed that SARS-CoV lacking the E gene (SARS-CoV-⌬E) is attenuated in several animal model systems. Here, we show that absence of the E protein resulted in reduced expression of proinflammatory cytokines, decreased numbers of neutrophils in lung infiltrates, diminished lung pathology, and increased mouse survival, suggesting that lung inflammation contributed to SARS-CoV virulence. Further, infection with SARS-CoV-⌬E resulted in decreased activation of NF-B compared to levels for the wild-type virus. Most important, treatment with drugs that inhibited NF-B activation led to a reduction in inflammation and lung pathology in both SARS-CoV-infected cultured cells and mice and significantly increased mouse survival after SARS-CoV infection. These data indicated that activation of the NF-B signaling pathway represents a major contribution to the inflammation induced after SARS-CoV infection and that NF-B inhibitors are promising antivirals in infections caused by SARS-CoV and potentially other pathogenic human coronaviruses.