Club cells surviving influenza A virus infection induce temporary nonspecific antiviral immunity

Abstract

A brief window of antigen-nonspecific protection has been observed after influenza A virus (IAV) infection. Although this temporary immunity has been assumed to be the result of residual nonspecific inflammation, this period of induced immunity has not been fully studied. Because IAV has long been characterized as a cytopathic virus (based on its ability to rapidly lyse most cell types in culture), it has been a forgone conclusion that directly infected cells could not be contributing to this effect. Using a Cre recombinase-expressing IAV, we have previously shown that club cells can survive direct viral infection. We show here not only that these cells can eliminate all traces of the virus and survive but also that they acquire a heightened antiviral response phenotype after surviving. Moreover, we experimentally demonstrate temporary nonspecific viral immunity after IAV infection and show that surviving cells are required for this phenotype. This work characterizes a virally induced modulation of the innate immune response that may represent a new mechanism to prevent viral diseases.influenza virus | RNA sequencing | alternative cell fate | antiviral immunity T here have been reports of a short period after influenza A virus (IAV) infection during which subsequent respiratory viral infection is restricted. This phenomenon has been shown experimentally in animal models (1-3), as well as in humans given the live-attenuated IAV vaccine in clinical studies (4-7), and has been postulated as a major factor in determining the rate of IAV antigenic drift (8). This temporary immunity has also been observed epidemically when the respiratory syncytial virus season was delayed as a result of the 2009 pandemic IAV outbreak occurring earlier than is normally seen with seasonal strains (9-11). Although observations of influenza-induced temporary immunity are well documented, how this protection is established is unknown.We have previously shown that respiratory epithelial cells (principally club cells) are infected by IAV and are capable of clearing infection and surviving for long periods in vivo (12). These surviving cells, characterized by an inflammatory transcriptional profile, contributed to bronchiolar epithelium damage. However, it was unclear why these cells would prolong an inflammatory state beyond the resolution of infection.In this report, we test the hypothesis that cells surviving IAV infection are involved in protecting the host from subsequent viral respiratory infections. We reasoned that the turnover of "survivor cells" could explain the temporary nature of IAVinduced antiviral immunity. We show that the cells that survive direct IAV infection are reprogrammed and exhibit an increased antiviral response to secondary infection and type I IFN. We also show that the overall immune response to secondary infection is different from the response to the primary infection. Finally, we demonstrate temporary, antigen-nonspecific viral immunity in the mouse model and show that surviving cells are required for this pr...

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