Promotion of Alpha/Beta Interferon Induction during In Vivo Viral Infection through Alpha/Beta Interferon Receptor/STAT1 System-Dependent and -Independent Pathways

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Abstract
Viruses and viral components can be potent inducers of alpha/beta interferons (IFN-α/β). In culture, IFN-α/β prime for their own expression, in response to viruses, through interferon regulatory factor 7 (IRF-7) induction. The studies presented here evaluated the requirements for functional IFN receptors and the IFN signaling molecule STAT1 in IFN-α/β induction during infections of mice with lymphocytic choriomeningitis virus (LCMV). At 24 h after infection, levels of induced IFN-α/β in serum were reduced 90 to 95% in IFN-α/β receptor-deficient (IFN-α/βR−/−) and STAT1−/−mice compared to those in wild-type mice. However, at 48 h, these mice showed elevated expression in the serum whereas IFN-α/β levels were still reduced >75% in IFN-α/βγR−/−mice even though the viral burden was heavy. Levels of IFN-β, IFN-α4, and non-IFN-α4 subtype mRNA expression correlated with IFN-α/β bioactivity, and all IFN-α/β subtypes were coincidentally detectable. IRF-7 mRNA was induced under conditions of IFN-α/β production, including late production in IFN-α/βR−/−mice. These data demonstrate that the presence of the virus alone is not sufficient to induce IFN-α/β during LCMV infection in vivo. Instead, autocrine amplification through the IFN-α/βR is necessary for optimal induction. In the absence of a functional IFN-α/βR, however, alternative mechanisms, independent of STAT1 but requiring a functional IFN-γR, take over.