Enhanced Atherogenesis Is Not an Obligatory Response to Systemic Herpesvirus Infection in the ApoE-Deficient Mouse: Comparison of Murine &ggr;-Herpesvirus-68 and Herpes Simplex Virus-1

Viral and bacterial infectious agents have been implicated in the etiology of atherosclerosis. We have previously shown that a &ggr;-herpesvirus can accelerate atherosclerosis in the apolipoprotein E–deficient (apoE−/−) mouse. To address whether a virally induced systemic immune response is sufficient to trigger enhanced atheroma formation, we infected apoE−/− mice with murine &ggr;-herpesvirus-68 (MHV-68) or herpes simplex virus-1 (HSV-1). In this study, we show that both viruses were able to induce a cell-mediated and humoral immune response in the apoE−/− mouse, which was sustained over a period of 24 weeks. Although intranasal or intraperitoneal infection with MHV-68 induced similar levels of virus-specific IgG1 and IgG2a antibodies in the serum of apoE−/− mice, those infected with HSV-1 showed higher anti–HSV-1 IgG2a compared with IgG1 antibody levels. In addition, viral message was not detected in the aortas of HSV-1–infected animals, whereas we have shown previously that MHV-68 mRNA can be detected in the aortas of infected mice as early as 5 days after infection. Compared with control mice, apoE−/− mice infected with MHV-68 showed accelerated atherosclerosis, whereas mice infected with HSV-1 did not. These data indicate that a systemic immune response to any particular infectious agent is insufficient to induce enhanced atherosclerosis in the apoE−/− mouse and point to specific infections or immune mechanisms that might be essential for virally enhanced atherogenesis.