IFIH1 and infection: Importantly, while breakdown of rRNA was also readily detectable in Mda5- and MAVS-deficient macrophages, rRNA remained intact in RNase L-deficient macrophages, demonstrating that infection of EndoU-deficient MHVH277A indeed results in the activation of the OAS-RNase L pathway and subsequent degradation of rRNA (Fig 5A; S2 Fig).