RSV immunizes bystander cells to IAV infection using interferons β and λ

Abstract

AbstractWe observed the interference between two prevalent respiratory viruses, respiratory syncytial virus (RSV) and influenza A virus (IAV, H1N1), and characterized its molecular underpinnings in alveolar epithelial cells (A549). We found that RSV induces higher interferon (IFN) β production than IAV and that IFNβ priming confers higher protection against infection with IAV than with RSV. Consequently, we focused on the sequential infection scheme: RSV-then-IAV. Using the A549 WT, IFNAR1 KO, IFNLR1 KO, and IFNAR1–IFNLR1 double KO cell lines we found that both IFNβ and IFNλ are necessary for maximum protection against subsequent infection. Immunostaining revealed that preinfection with RSV partitions the cell population into a subpopulation susceptible to subsequent infection with IAV and an IAV-proof subpopulation. Strikingly, the susceptible cells turned out to be those already compromised and efficiently expressing RSV, whereas the bystander, interferon-primed cells are resistant to IAV infection. Thus, the virus–virus exclusion at the cell population level is not realized through a direct competition for a shared ecological niche (single cell) but rather achieved with the involvement of specific cytokines induced within the host innate immune response.Author summaryAfter being challenged with a pathogen, infected cells warn bystander cells about the potential threat by synthesizing and secreting cytokines, especially interferons. In this way, the not yet infected but warned cells are given an opportunity to reinforce their defense mechanisms before they encounter the pathogen replicating in the infected cells whose defense mechanisms have been overcome. Consequently, cell population is partitioned into the cells that may be more prone to infection with another pathogen and the cells that may be expected to be resistant to another pathogen. By studying at the single-cell level the sequential infection with two prevalent respiratory viruses, respiratory syncytial virus (RSV) and influenza A virus (IAV), we showed that the interferon-mediated resistance induced by infection with RSV protects non-infected cells from infection with IAV. The cells compromised by RSV turned out however to be susceptible to invasion of IAV. This demonstrates that, even in the absence of within-cell viral competition, the innate immune response can induct viral interference between primary infection with RSV and secondary infection with IAV.