Essential cell-autonomous role for interferon (IFN) regulatory factor 1 in IFN-γ-mediated inhibition of norovirus replication in macrophages.

Noroviruses (NVs) cause the majority of cases of epidemic nonbacterial gastroenteritis worldwide and contribute to endemic enteric disease. However, the molecular mechanisms responsible for immune control of their replication are not completely understood. Here we report that the transcription factor interferon regulatory factor 1 (IRF-1) is required for control of murine NV (MNV) replication and pathogenesis in vivo. This led us to studies documenting a cell-autonomous role for IRF-1 in gamma interferon (IFN-γ)-mediated inhibition of MNV replication in primary macrophages. This role of IRF-1 in the inhibition of MNV replication by IFN-γ is independent of IFN-αß signaling. While the signal transducer and activator of transcription STAT-1 was also required for IFN-γ-mediated inhibition of MNV replication in vitro, class II transactivator (CIITA), interferon regulatory factor 3 (IRF-3), and interferon regulatory factor 7 (IRF-7) were not required. We therefore hypothesized that there must be a subset of IFN-stimulated genes (ISGs) regulated by IFN-γ in a manner dependent only on STAT-1 and IRF-1. Analysis of transcriptional profiles of macrophages lacking various transcription factors confirmed this hypothesis. These studies identify a key role for IRF-1 in IFN-γ-dependent control of norovirus infection in mice and macrophages.

Specific mutation of a gammaherpesvirus-expressed antigen in response to CD8 T cell selection in vivo.

Herpesviruses are thought to be highly genetically stable, and their use as vaccine vectors has been proposed. However, studies of the human gammaherpesvirus, Epstein-Barr virus, have found viral isolates containing mutations in HLA class I-restricted epitopes. Using murine gammaherpesvirus 68 expressing ovalbumin (OVA), we examined the stability of a gammaherpesvirus antigenic locus under strong CD8 T cell selection in vivo. OVA-specific CD8 T cells selected viral isolates containing mutations in the OVA locus but minimal alterations in other genomic regions. Thus, a CD8 T cell response to a gammaherpesvirus-expressed antigen that is not essential for replication or pathogenesis can result in selective mutation of that antigen in vivo. This finding may have relevance for the use of herpesvirus vectors for chronic antigen expression in vivo.

Identification and sequencing of a novel rodent gammaherpesvirus that establishes acute and latent infection in laboratory mice.

Gammaherpesviruses encode numerous immunomodulatory molecules that contribute to their ability to evade the host immune response and establish persistent, lifelong infections. As the human gammaherpesviruses are strictly species specific, small animal models of gammaherpesvirus infection, such as murine gammaherpesvirus 68 (γHV68) infection, are important for studying the roles of gammaherpesvirus immune evasion genes in in vivo infection and pathogenesis. We report here the genome sequence and characterization of a novel rodent gammaherpesvirus, designated rodent herpesvirus Peru (RHVP), that shares conserved genes and genome organization with γHV68 and the primate gammaherpesviruses but is phylogenetically distinct from γHV68. RHVP establishes acute and latent infection in laboratory mice. Additionally, RHVP contains multiple open reading frames (ORFs) not present in γHV68 that have sequence similarity to primate gammaherpesvirus immunomodulatory genes or cellular genes. These include ORFs with similarity to major histocompatibility complex class I (MHC-I), C-type lectins, and the mouse mammary tumor virus and herpesvirus saimiri superantigens. As these ORFs may function as immunomodulatory or virulence factors, RHVP presents new opportunities for the study of mechanisms of immune evasion by gammaherpesviruses.