| Summary: | Summary: Type I interferon (IFNα/β) pathways are fine-tuned to elicit antiviral protection while minimizing immunopathology; however, the initiating stimuli, target tissues, and underlying mechanisms are unclear. Using models of physiological and dysregulated IFNα/β receptor (IFNAR1) surface expression, we show here that IFNAR1-dependent signals set the steady-state IFN signature in both hematopoietic and stromal cells. Increased IFNAR1 levels promote a lung environment refractory to early influenza virus replication by elevating the baseline interferon signature. Commensal microbiota drive the IFN signature specifically in lung stroma, as shown by antibiotic treatment and fecal transplantation. Bone marrow chimera experiments identify lung stromal cells as crucially important for early antiviral immunity and stroma-immune cell interaction for late antiviral resistance. We propose that the microbiota-driven interferon signature in lung epithelia impedes early virus replication and that IFNAR1 surface levels fine-tune this signature. Our findings highlight the interplay between bacterial and viral exposure, with important implications for antibiotic use. : Bradley, Finsterbusch, et al. identify lung stroma as the target of microbiota-driven signals that set the interferon signature in these cells. Antibiotic treatment reduces gut microbiota and the lung stromal interferon signature and facilitates early influenza virus replication in lung epithelia, effects that can be reversed by fecal transplantation. Keywords: type I interferon (IFN), tonic IFN signaling, lung, microbiota, influenza, anti-viral protection, gut, antibiotics
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