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

Abstract

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. H uman cytomegalovirus (HCMV) is a betaherpesvirus which establishes a lifelong latent infection in immunocompetenthosts. Latent HCMV is present in the majority of people worldwide, but the primary infection is usually asymptomatic. The primary infection is well contained by the immune cells, such as natural killer (NK) cells and T cells, which also prevent viral reactivation from latency (1, 2).Their activation depends on cross talk with dendritic cells (DC) (3, 4), and this interaction plays an important role in CMV control (5-7). The direct effect of DC on viral replication remains, however, unclear.In immunocompromised hosts, like AIDS patients or people undergoing transplantation, the virus cannot be contained, and its reactivation from latency has been associated with severe disease (8). Therefore, to develop new therapeutic approaches against CMV disease, it is exceedingly important to understand the immune mechanisms that drive the virus into latency.Murine cytomegalovirus (MCMV) is a natural pathogen of the mouse. It shows numerous analogies in latency and reactivation to the human virus, and its genome displays substantial similarity to the HCMV one (9). Therefore, MCMV is a widely used model for CMV infection and immunity (10)(11)(12).During primary infection, MCMV infects various different cell types, such as macrophages and DC but also nonhematopoietic cells, including endothelial and epithelial cells (13). On the other hand, the establishment of latency appears to be restricted to certain cell types. Latent HCMV was found in blood monocytes and in progenitor cells of the myeloid lineage (14-19), whereas liver sinusoidal endothelial cells (LSEC) were shown to be a site of MCMV latency and reactivation (20, 21), although myeloid cells might also present a latent reservoir in the mouse (22, 23).

Conventional Dendritic Cells Confer Protection against Mouse Cytomegalovirus Infection via TLR9 and MyD88 Signaling

“…Specifically, cDCs control independent arms of NK cell function during acute MCMV infection by driving NK cell IFN-g and acquisition of cytotoxic granules via IL-12 and IL-15, respectively. Our data explain mechanistically why depletion of CD11c + DCs significantly increases the viral load in primary organs, as recently demonstrated (Holzki et al, 2015). Altogether, our results show that in the absence of pDCs, TLR9 and MyD88 signaling in cDCs is mandatory for MCMV clearance and NK cell effector function during the early phase of MCMV infection.…”

One Step Ahead: Herpesviruses Light the Way to Understanding Interferon-Stimulated Genes (ISGs)

“…While KSHV vIRFs inhibit IFN signalling, type I IFN is not always detrimental for herpesviruses as it plays an important role for the maintenance of latency (Zhang et al, 2004;De Regge et al, 2010;Dag et al, 2014;Holzki et al, 2015). In line with these findings, vIRF2 has been recently described to manipulate the innate immune response.…”

Peptide Processing Is Critical for T-Cell Memory Inflation and May Be Optimized to Improve Immune Protection by CMV-Based Vaccine Vectors

“…Since the HGIRNASFI epitope located at its native site is poorly processed and presented on infected fibroblasts [26], we considered that the improved response to MCMV M45Cterm might be due to the availability of the peptide itself on MHC-I molecules. Hence, to measure the presentation of HGIRNASFI on LSECs, we analyzed the IFNγ response of a HGIRNASFI-specific CD8 T-cell line (CTL) upon co-culture with a recently published LSECs line [27]. LSECs infected with the control virus (MCMV M45I->A ) or with MCMV WT did not activate M45-specific CTL, whereas the MCMV M45Cterm virus induced a robust activation (Fig 5B, upper row ).…”

“…TC-1 tumor cells were grown as described [22]. LSECs from C57BL/6 mice were generated and maintained as described [27]. C57BL/6 murine embryonic fibroblasts (MEFs) were prepared and maintained as described previously [49].…”