IFN--mediated control of SARS-CoV-2 infection through nitric oxide

Introduction The COVID-19 pandemic has highlighted the need to identify mechanisms of antiviral host defense against SARS-CoV-2. One such mediator is interferon-g (IFN-gamma), which, when administered to infected patients, is reported to result in viral clearance and resolution of pulmonary symptoms. IFN-gamma treatment of a human lung epithelial cell line triggered an antiviral activity against SARS-CoV-2, yet the mechanism for this antiviral response was not identified. Methods Given that IFN-gamma has been shown to trigger antiviral activity via the generation of nitric oxide (NO), we investigated whether IFN-gamma induction of antiviral activity against SARS-CoV-2 infection is dependent upon the generation of NO in human pulmonary epithelial cells. We treated the simian epithelial cell line Vero E6 and human pulmonary epithelial cell lines, including A549-ACE2, and Calu-3, with IFN-gamma and observed the resulting induction of NO and its effects on SARS-CoV-2 replication. Pharmacological inhibition of inducible nitric oxide synthase (iNOS) was employed to assess the dependency on NO production. Additionally, the study examined the effect of interleukin-1b (IL-1 beta) on the IFN-g-induced NO production and its antiviral efficacy. Results Treatment of Vero E6 cells with IFN-gamma resulted in a dose-responsive induction of NO and an inhibitory effect on SARS-CoV-2 replication. This antiviral activity was blocked by pharmacologic inhibition of iNOS. IFN-gamma also triggered a NO-mediated antiviral activity in SARS-CoV-2 infected human lung epithelial cell lines A549-ACE2 and Calu-3. IL-1 beta enhanced IFN-gamma induction of NO, but it had little effect on antiviral activity. Discussion Given that IFN-g has been shown to be produced by CD8+ T cells in the early response to SARS-CoV-2, our findings in human lung epithelial cell lines, of an IFN-gamma-triggered, NO-dependent, links the adaptive immune response to an innate antiviral pathway in host defense against SARS-CoV-2. These results underscore the importance of IFN-gamma and NO in the antiviral response and provide insights into potential therapeutic strategies for COVID-19.