DNA virus infection can elicit the DNA damage response in host cells, including ATM kinase activation and H2AX phosphorylation. This is considered to be the host cell response to replicating viral DNA. In contrast, we show that during infection of macrophages murine gamma-herpesvirus 68 (gammaHV68) actively induces H2AX phosphorylation by expressing a viral kinase (orf36). GammaHV68-encoded orf36 kinase and its EBV homolog, BGLF4, induce H2AX phosphorylation independently of other viral genes. The process requires the kinase domain of Orf36 and is enhanced by ATM. Orf36 is important for gammaHV68 replication in infected animals, and orf36, H2AX, and ATM are all critical for efficient gammaHV68 replication in primary macrophages. Thus, activation of proximal components of the DNA damage signaling response is an active viral kinase-driven strategy required for efficient gamma-herpesvirus replication.

Human gammaherpesvirus infections are associated with development of lymphoproliferative disease. Understanding of the mechanisms of gammaherpesvirus lymphomagenesis during chronic infection in a natural host has been limited by the exquisite species specificity of human gammaherpesviruses and the expense of primates. Murine gammaherpesvirus ␥HV68 is genetically and biologically related to human gammaherpesviruses and herpesvirus saimiri and has been reported to be associated with lymphoproliferative disease in mice (N. P. Sunil-Chandra, J. Arno, J. Fazakerley, and A. A. Nash, Am. J. Pathol. 145:818-826, 1994). We report the development of an animal model of ␥HV68 lymphomagenesis in BALB/c ␤2 microglobulin-deficient mice (BALB ␤2m ؊/؊ ). ␥HV68 infection induced two lymphoproliferative lesions: B-cell lymphoma and atypical lymphoid hyperplasia (ALH). ALH lesion histology resembled lesions of Epstein-Barr virus-associated posttransplant lymphoproliferative disease and was characterized by the abnormal infiltration of the white pulp with cells expressing the plasma cell marker CD138. Lymphomas observed in ␥HV68-infected animals were B220 ؉ /CD3 ؊ large-cell lymphomas. ␥HV68-infected cells were common in ALH lesions as measured by in situ hybridization with a probe specific for viral tRNAs (vtRNAs), but they were scarce in ␥HV68-infected spleens with normal histology. Unlike ALH lesions, ␥HV68 vtRNA-positive cells were rare in lymphomas. ␥HV68 infection of BALB ␤2m ؊/؊ mice results in lymphoproliferation and lymphoma, providing a valuable tool for identifying viral and host genes involved in gammaherpesvirus-associated malignancies. Our findings suggest that ␥HV68 induces lymphomas via hit-and-run oncogenesis, paracrine effects, or stimulation of chronic inflammation.

c Nitric oxide, produced in pancreatic ␤ cells in response to proinflammatory cytokines, plays a dual role in the regulation of ␤-cell fate. While nitric oxide induces cellular damage and impairs ␤-cell function, it also promotes ␤-cell survival through activation of protective pathways that promote ␤-cell recovery. In this study, we identify a novel mechanism in which nitric oxide prevents ␤-cell apoptosis by attenuating the DNA damage response (DDR). Nitric oxide suppresses activation of the DDR (as measured by ␥H2AX formation and the phosphorylation of KAP1 and p53) in response to multiple genotoxic agents, including camptothecin, H 2 O 2 , and nitric oxide itself, despite the presence of DNA damage. While camptothecin and H 2 O 2 both induce DDR activation, nitric oxide suppresses only camptothecin-induced apoptosis and not H 2 O 2 -induced necrosis. The ability of nitric oxide to suppress the DDR appears to be selective for pancreatic ␤ cells, as nitric oxide fails to inhibit DDR signaling in macrophages, hepatocytes, and fibroblasts, three additional cell types examined. While originally described as the damaging agent responsible for cytokine-induced ␤-cell death, these studies identify a novel role for nitric oxide as a protective molecule that promotes ␤-cell survival by suppressing DDR signaling and attenuating DNA damage-induced apoptosis.

During chronic viral infection, the inflammatory function of CD4 T-cells becomes gradually attenuated. Concurrently, Th1 cells progressively acquire the capacity to secrete the cytokine IL-10, a potent suppressor of antiviral T cell responses. To determine the transcriptional changes that underlie this adaption process, we applied a single-cell RNA-sequencing approach and assessed the heterogeneity of IL-10-expressing CD4 T-cells during chronic infection. Here we show an IL-10-producing population with a robust Tfh-signature. Using IL-10 and IL-21 double-reporter mice, we further demonstrate that IL-10+IL-21+co-producing Tfh cells arise predominantly during chronic but not acute LCMV infection. Importantly, depletion of IL-10+IL-21+co-producing CD4 T-cells or deletion of Il10 specifically in Tfh cells results in impaired humoral immunity and viral control. Mechanistically, B cell-intrinsic IL-10 signaling is required for sustaining germinal center reactions. Thus, our findings elucidate a critical role for Tfh-derived IL-10 in promoting humoral immunity during persistent viral infection.

Gammaherpesviruses are ubiquitous pathogens that establish a lifelong infection and are associated with cancer. In spite of the high seroprevalence of infection, the risk factors that predispose the host toward gammaherpesvirus-induced malignancies are still poorly understood. Interferon (IFN) regulatory factor 1 (IRF-1) is a tumor suppressor that is also involved in the regulation of innate and adaptive immune responses. On the basis of its biology, IRF-1 represents a plausible host factor to attenuate gammaherpesvirus infection and tumorigenesis. In this study, we show that IRF-1 restricts gammaherpesvirus replication in primary macrophages, a physiologically relevant immune cell type. In spite of the known role of IRF-1 in stimulating type I IFN expression, induction of a global type I IFN response was similar in IRF-1-deficient and -proficient macrophages during gammaherpesvirus infection. However, IRF-1 was required for optimal expression of cholesterol-25-hydroxylase, a host enzyme that restricted gammaherpesvirus replication in primary macrophages and contributed to the antiviral effects of IRF-1. In summary, the current study provides an insight into the mechanism by which IRF-1 attenuates gammaherpesvirus replication in primary immune cells, a mechanism that is likely to contribute to the antiviral effects of IRF-1 in other virus systems. IMPORTANCEInterferon regulatory factor 1 (IRF-1) is a transcription factor that regulates innate and adaptive immune responses and functions as a tumor suppressor. IRF-1 restricts the replication of diverse viruses; however, the mechanisms responsible for the antiviral effects of IRF-1 are still poorly understood. Gammaherpesviruses are ubiquitous pathogens that are associated with the induction of several malignancies. Here we show that IRF-1 expression attenuates gammaherpesvirus replication in primary macrophages, in part by increasing expression of cholesterol-25-hydroxylase (CH25H). CH25H and its product, 25-hydroxycholesterol, restrict replication of diverse virus families. Thus, our findings offer an insight into the mechanism by which IRF-1 attenuates the replication of gammaherpesviruses, a mechanism that is likely to be applicable to other virus systems.