Novel Cell Type–Specific Antiviral Mechanism of Interferon γ Action in Macrophages

Abstract

Interferon (IFN)-γ and macrophages (Mϕ) play key roles in acute, persistent, and latent murine cytomegalovirus (MCMV) infection. IFN-γ mechanisms were compared in embryonic fibroblasts (MEFs) and bone marrow Mϕ (BMMϕ). IFN-γ inhibited MCMV replication in a signal transducer and activator of transcription (STAT)-1α–dependent manner much more effectively in BMMϕ (∼100-fold) than MEF (5–10-fold). Although initial STAT-1α activation by IFN-γ was equivalent in MEF and BMMϕ, microarray analysis demonstrated that IFN-γ regulates different sets of genes in BMMϕ compared with MEFs. IFN-γ inhibition of MCMV growth was independent of known mechanisms involving IFN-α/β, tumor necrosis factor α, inducible nitric oxide synthase, protein kinase RNA activated (PKR), RNaseL, and Mx1, and did not involve IFN-γ–induced soluble mediators. To characterize this novel mechanism, we identified the viral targets of IFN-γ action, which differed in MEF and BMMϕ. In BMMϕ, IFN-γ reduced immediate early 1 (IE1) mRNA during the first 3 h of infection, and significantly reduced IE1 protein expression for 96 h. Effects of IFN-γ on IE1 protein expression were independent of RNaseL and PKR. In contrast, IFN-γ had no significant effects on IE1 protein or mRNA expression in MEFs, but did decrease late gene mRNA expression. These studies in primary cells define a novel mechanism of IFN-γ action restricted to Mϕ, a cell type key for MCMV pathogenesis and latency.

Viperin (cig5), an IFN-inducible antiviral protein directly induced by human cytomegalovirus

“…However, the mechanism of IFN protection against CMV at the molecular level is not known. The best studied IFN-inducible antiviral proteins, such as double-stranded RNA-dependent protein kinase, Mx, and ribonuclease L, seem not to be involved (10).…”

Murine cytomegalovirus paralyzes macrophages by blocking IFNγ-induced promoter assembly

“…Bone marrow M (BMM ) lacking IFN␣␤ receptor-1 (IFNAR1) chain (IFNAR1Ϫ͞Ϫ mice) and MCMV (ATCC no. VR-194, Lot 10) were cultured as described (6,10,15,19). BMM were infected for 1 h at a multiplicity of infection (moi) of 5 in 2 ml of media at 37°C and then treated with or without 100 units͞ml murine IFN␥ (R & D Systems) for 6, 24, and 48 h. UV inactivation of MCMV by using a NuAire (Plymouth, MN) laminar flow hood UV bulb for 30 min resulted in a Ͼ10 7 fold decrease in titer and an absence of viral gene expression by quantitative RT-PCR (qRT-PCR) analysis.…”

“…This reliance on M creates a problem for CMVs, because M are activated by antiviral cytokines such as IFN␥ in vivo (8,9) and are critical for control of MCMV infection (2). The M activating cytokine IFN␥ is crucial for controlling persistent MCMV replication in vivo (9) and reversibly inhibits reactivation of MCMV from latency, in part by blocking viral growth (9)(10)(11). M are activated to express increased MHC class II in vivo in response to IFN␥ during MCMV infection (8,9,12), and IFN␥ treatment of M decreases HCMV and MCMV growth up to 100-fold (10,13).…”

Mouse cytomegalovirus inhibits beta interferon (IFN-β) gene expression and controls activation pathways of the IFN-β enhanceosome

“…The CMV interference with IFN production is complemented by further independent strategies counteracting the efficacy of IFNs. Through establishing a state of IFN receptor unresponsiveness by disrupting Jak/STAT signalling and antiviral gene expression (Heise et al, 1998;Presti et al, 2001;Zimmermann et al, 2005) MCMV builds protected 'virus factories' enabling efficient viral replication even in the presence of significant concentrations of IFNs. On the other hand MCMV triggering of IFN producing capacities in pDCs could be essential for the augmenting of natural killer and cytotoxic T lymphocyte responses attaining a balanced virus-host relationship.…”