Murine Cytomegalovirus Infection Inhibits IFNγ-Induced MHC Class II Expression on Macrophages: The Role of Type I Interferon

Abstract

Macrophage (M phi) activation, as measured by cell surface expression of MHC class II, was examined during infection of immunocompetent and immunocompromised mice with murine cytomegalovirus (MCMV). Intraperitoneal infection of CB17 SCID mice with 10(6) PFU of MCMV elicited a large population of M phi which expressed low levels of MHC class II. This was surprising since infection of SCID mice with lower doses (e.g., 10(4) PFU) of MCMV elicits M phi expressing high levels of MHC class II (M. T. Heise and H. W. Virgin, J. Virol. (1995) 69, 904-909). In vivo administration of recombinant mouse IFN gamma resulted in high levels of MHC class II expression on M phi from control but not MCMV-infected SCID mice, suggesting that MCMV infection generates a state in which IFN gamma is not effective at activating M phi. The effect of MCMV infection was MHC class II specific, since MHC class I and ICAM-1 levels were increased on M phi expressing low levels of MHC class II. Interference with IFN gamma action was not due to productive or abortive infection of M phi. This suggested that MCMV infection induces a soluble factor that alters M phi responsiveness to IFN gamma. Infection of SCID mice with 10(6) PFU of MCMV induced higher levels of serum IFN alpha beta (one candidate for inhibition of IFN gamma induction of MHC class II expression) than infection with 10(4) PFU. We therefore evaluated the role of MCMV-induced IFN alpha beta on IFN gamma responses of bone marrow-derived (BMM phi) or thioglycollate-elicited M phi in vitro. Infection of normal M phi with MCMV at a low m.o.i. (0.1 to 0.2) impaired IFN gamma-mediated induction of M phi MHC class II expression, but not MHC class I expression. Inhibition of IFN gamma responses was not observed in M phi from mice with a null mutation in the IFN alpha beta receptor (IFN alpha beta R-/-). To test the in vivo relevance of virus-induced IFN alpha beta to IFN gamma-mediated responses, the kinetics of MHC class II induction during MCMV infection of IFN alpha beta R-/- mice was evaluated. MCMV-infected IFN alpha beta R-/- mice mounted an earlier M phi MHC class II response than normal mice. We conclude that MCMV infection specifically impairs IFN gamma-mediated MHC class II expression on M phi and that induction of IFN alpha beta is one mechanism by which this inhibition occurs.

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.…”

“…M infection was assessed by immunofluorescence by counting Ͼ200 cells after staining for IE1 protein (10). Fluorescence-activated cell sorting (FACS) analysis was performed as described (15,19) by using 2G9-phycoerythrin (PE) (MHC class II) and stem cell antigen-1 (Sca-1)-PE (PharMingen).…”

“…M MHC class II induced during MCMV infection requires IFN␥ (8). Mice lacking a functional IFN␣␤ receptor (IFNAR1Ϫ͞Ϫ) were used, because IFN␣␤ expression inhibits M activation by IFN␥ in vivo (19). Both F4͞80 positive M and F4͞80 negative non-M were infected with MCMV.…”

“…Similarly, M play a key role in MCMV infection as cells that disseminate the virus, cells that are critical to host defense against the virus, and cells that harbor latent virus during chronic infection (1)(2)(3)(4)(5)(6)(7). The link between M and IFN␥ is especially important because IFN␥ is uniquely potent at inducing an antiviral state in M compared with other cells (10), and IFN␥ is essential for activating M during MCMV infection in vivo (8,19). For these reasons, we speculate that the inhibition of IFN␥-induced differentiation in M is especially critical for efficient MCMV survival in the host.…”

“…For example, infection with HCMV or MCMV effectively inhibits IFN␥-induced antigen presentation by MHC class II by inhibiting IFN␥ induction of genes involved in antigen presentation (15,(19)(20)(21).…”