Type I Interferon Released by Myeloid Dendritic Cells Reversibly Impairs Cytomegalovirus Replication by Inhibiting Immediate Early Gene Expression

Cytomegalovirus (CMV) is a ubiquitous beta-herpesvirus whose reactivation from latency is a major cause of morbidity and mortality in immunocompromised hosts. Mouse CMV (MCMV) is a well-established model virus to study virus-host interactions. We showed in this study that the CD8-independent antiviral function of myeloid dendritic cells (mDC) is biologically relevant for the inhibition of MCMV replication in vivo and in vitro. In vivo ablation of CD11c(+) DC resulted in higher viral titers and increased susceptibility to MCMV infection in the first 3 days postinfection. We developed in vitro coculture systems in which we cocultivated MCMV-infected endothelial cells or fibroblasts with T cell subsets and/or dendritic cells. While CD8 T cells failed to control MCMV replication, bone marrow-derived mDC reduced viral titers by a factor of up to 10,000. Contact of mDC with the infected endothelial cells was crucial for their antiviral activity. Soluble factors secreted by the mDC blocked MCMV replication at the level of immediate early (IE) gene expression, yet the viral lytic cycle reinitiated once the mDC were removed from the cells. On the other hand, the mDC did not impair MCMV replication in cells deficient for the interferon (IFN) alpha/beta receptor (IFNAR), arguing that type I interferons were critical for viral control by mDC. In light of our recent observation that type I IFN is sufficient for the induction of latency immediately upon infection, our results imply that IFN secreted by mDC may play an important role in the establishment of CMV latency. IMPORTANCE Numerous studies have focused on the infection of DC with cytomegaloviruses and on the establishment of latency within them. However, almost all of these studies have relied on the infection of DC monocultures in vitro, whereas DC are just one among many cell types present in an infection site in vivo. To mimic this aspect of the in vivo situation, we cocultured DC with infected endothelial cells or fibroblasts. Our data suggest that direct contact with virus-infected endothelial cells activates CD11c(+) DC, which leads to reversible suppression of MCMV replication at the level of IE gene expression by a mechanism that depends on type I IFN. The effect matches the formal definition of viral latency. Therefore, our data argue that the interplay of dendritic cells and infected neighboring cells might play an important role in the establishment of viral latency.