A mouse model for infectious mononucleosis

Understanding the link between neurotropic viruses, BBB permeability, and MS pathogenesis

Neurotropic viruses can infiltrate the CNS by crossing the blood-brain barrier (BBB) through various mechanisms including paracellular, transcellular, and "Trojan horse" mechanisms during leukocyte diapedesis. These viruses belong to several families, including retroviruses; human immunodeficiency virus type 1 (HIV-1), flaviviruses; Japanese encephalitis (JEV); and herpesviruses; herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV), and mouse adenovirus 1 (MAV-1). For entering the brain, viral proteins act upon the tight junctions (TJs) between the brain microvascular endothelial cells (BMECs). For instance, HIV-1 proteins, such as glycoprotein 120, Nef, Vpr, and Tat, disrupt the BBB and generate a neurotoxic effect. Recombinant-Tat triggers amendments in the BBB by decreasing expression of the TJ proteins such as claudin-1, claudin-5, and zona occludens-1 (ZO-1). Thus, the breaching of BBB has been reported in myriad of neurological diseases including multiple sclerosis (MS). Neurotropic viruses also exhibit molecular mimicry with several myelin sheath proteins, i.e., antibodies against EBV nuclear antigen 1 (EBNA1) aa411-426 cross-react with MBP and EBNA1 aa385-420 was found to be associated with MS risk haplotype HLA-DRB1*150. Notably, myelin protein epitopes (PLP139-151, MOG35-55, and MBP87-99) are being used to generate model systems for MS such as experimental autoimmune encephalomyelitis (EAE) to understand the disease mechanism and therapeutics. Viruses like Theiler's murine encephalomyelitis virus (TMEV) are also commonly used to generate EAE. Altogether, this review provide insights into the viruses' association with BBB leakiness and MS along with possible mechanistic details which could potentially use for therapeutics.

Host Genetic Variation Has a Profound Impact on Immune Responses Mediating Control of Viral Load in Chronic Gammaherpesvirus Infection

Chronic infection with the gammaherpesvirus EBV is a risk factor for several autoimmune diseases, and poor control of EBV viral load and enhanced anti-EBV responses elevate this risk further. However, the role of host genetic variation in the regulation of immune responses to chronic gammaherpesvirus infection and control of viral replication remains unclear. To address this question, we infected C57BL/6J (B6) and genetically divergent wild-derived inbred PWD/PhJ (PWD) mice with murine gammaherpesvirus-68 (MHV-68), a gammaherpesvirus similar to EBV, and determined the effect of latent gammaherpesvirus infection on the CD4 T cell transcriptome. Chronic MHV-68 infection of B6 mice resulted in a dramatic upregulation of genes characteristic of a cytotoxic Th cell phenotype, including Gzmb, Cx3cr1, Klrg1, and Nkg7, a response that was highly muted in PWD mice. Flow cytometric analyses revealed an expansion of CX3CR1+KLRG1+ cytotoxic Th cell-like cells in B6 but not PWD mice. Analysis of MHV-68 replication demonstrated that in spite of muted adaptive responses, PWD mice had superior control of viral load in lymphoid tissue, despite an absence of a defect in MHV-68 in vitro replication in PWD macrophages. Depletion of NK cells in PWD mice, but not B6 mice, resulted in elevated viral load, suggesting genotype-dependent NK cell involvement in MHV-68 control. Taken together, our findings demonstrate that host genetic variation can regulate control of gammaherpesvirus replication through disparate immunological mechanisms, resulting in divergent long-term immunological sequelae during chronic infection.

Involvement of TLR4 in Acute Hepatitis Associated with Airway Infection of Murine γ-Herpesvirus 68

Extrahepatic viral infections are often accompanied by acute hepatitis, as evidenced by elevated serum liver enzymes and intrasinusoidal infiltration of CD8+ T cells, without direct infection of the liver. An example is infectious mononucleosis caused by primary infection with EBV. Previously, we demonstrated that airway infection of mice with murine γ-herpesvirus 68 (MHV68), a murine model of EBV, caused liver inflammation with elevated serum liver enzymes and intrahepatic infiltration of IFN-γ-producing CD8+ T cells and NK cells. Mechanistically, the expression of the CXCR3-ligand chemokines, which are commonly induced by IFN-γ and attract IFN-γ-producing Th1-type cells via CXCR3, was upregulated in the liver. Importantly, the liver inflammation was suppressed by oral neomycin, an intestine-impermeable aminoglycoside, suggesting an involvement of some products from the intestinal microbiota. In this study, we showed that the liver inflammation and the expression of the CXCR3-ligand chemokines in the liver were effectively ameliorated by i.p. administration of anti-TLR4 mAb or C34, a TLR4 blocker, as well as in TLR4-deficient mice. Conversely, intrarectal inoculation of Escherichia coli as an extraintestinal source of LPS aggravated liver inflammation in MHV68-infected mice with increased expression of the CXCR3-ligand chemokines in the liver. In contrast, the lung inflammation in MHV68-infected mice was not affected by oral neomycin, i.p. administration of C34, or TLR4 deficiency. Collectively, the LPS-TLR4 pathway plays a pivotal role in the liver inflammation of MHV68-infected mice at least in part by upregulating the CXCR3-ligand chemokines in the liver.

The innate and T-cell mediated immune response during acute and chronic gammaherpesvirus infection

Immediately after entry into host cells, viruses are sensed by the innate immune system, leading to the activation of innate antiviral effector mechanisms including the type I interferon (IFN) response and natural killer (NK) cells. This innate immune response helps to shape an effective adaptive T cell immune response mediated by cytotoxic T cells and CD4+ T helper cells and is also critical for the maintenance of protective T cells during chronic infection. The human gammaherpesvirus Epstein-Barr virus (EBV) is a highly prevalent lymphotropic oncovirus that establishes chronic lifelong infections in the vast majority of the adult population. Although acute EBV infection is controlled in an immunocompetent host, chronic EBV infection can lead to severe complications in immunosuppressed patients. Given that EBV is strictly host-specific, its murine homolog murid herpesvirus 4 or MHV68 is a widely used model to obtain in vivo insights into the interaction between gammaherpesviruses and their host. Despite the fact that EBV and MHV68 have developed strategies to evade the innate and adaptive immune response, innate antiviral effector mechanisms still play a vital role in not only controlling the acute infection but also shaping an efficient long-lasting adaptive immune response. Here, we summarize the current knowledge about the innate immune response mediated by the type I IFN system and NK cells, and the adaptive T cell-mediated response during EBV and MHV68 infection. Investigating the fine-tuned interplay between the innate immune and T cell response will provide valuable insights which may be exploited to design better therapeutic strategies to vanquish chronic herpesviral infection.

Type I Interferon Signaling Controls Gammaherpesvirus Latency In Vivo

Gammaherpesviruses, such as Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, are important human pathogens involved in lymphoproliferative disorders and tumorigenesis. Herpesvirus infections are characterized by a biphasic cycle comprised of an acute phase with lytic replication and a latent state. Murine gammaherpesvirus 68 (MHV-68) is a well-established model for the study of lytic and latent life cycles in the mouse. We investigated the interplay between the type I interferon (IFN)-mediated innate immune response and MHV-68 latency using sensitive bioluminescent reporter mice. Adoptive transfer of latently infected splenocytes into type I IFN receptor-deficient mice led to a loss of latency control. This was revealed by robust viral propagation and dissemination of MHV-68, which coincided with type I IFN reporter induction. Despite MHV-68 latency control by IFN, the continuous low-level cell-to-cell transmission of MHV-68 was detected in the presence of IFN signaling, indicating that IFN cannot fully prevent viral dissemination during latency. Moreover, impaired type I IFN signaling in latently infected splenocytes increased the risk of virus reactivation, demonstrating that IFN directly controls MHV-68 latency in infected cells. Overall, our data show that locally constrained type I IFN responses control the cellular reservoir of latency, as well as the distribution of latent infection to potential new target cells.

Influence of Type I Interferons in Gammaherpesvirus-68 and Its Influence on EAE Enhancement

Epstein-Barr virus (EBV) has been identified as a putative trigger of multiple sclerosis (MS). Previously, we reported that mice latently infected with murine gammaherpesvirus 68 (γHV-68), the murine homolog to EBV, and induced for experimental autoimmune encephalomyelitis (EAE), developed an enhanced disease more reminiscent of MS. These prior results showed that expression of CD40 on CD11b⁺CD11c⁺ cells in latently infected mice was required to prime the strong Th1 response driving disease as well as decreasing Treg frequencies in the periphery and CNS. Subsequent work demonstrated that transfer of B cells from latently infected mice was sufficient to enhance disease. Herein, we show that B cells from infected mice do not need type I IFN signaling to drive a strong Th1 response, yet are important in driving infiltration of the CNS by CD8⁺ T cells. Given the importance of type I IFNs in MS, we used IFNARko mice in order to determine if type I IFN signaling was important in the enhancement of EAE in latently infected mice. We found that while type I IFNs are important for the control of γHV-68 infection and maintenance of latency, they do not have a direct effect in the development of enhanced EAE.

Lytic Replication and Reactivation from B Cells Is Not Required for Establishing or Maintaining Gammaherpesvirus Latency In Vivo

Gammaherpesviruses (GHVs) are lymphotropic tumor viruses with a biphasic infectious cycle. Lytic replication at the primary site of infection is necessary for GHVs to spread throughout the host and establish latency in distal sites. Dissemination is mediated by infected B cells that traffic hematogenously from draining lymph nodes to peripheral lymphoid organs, such as the spleen. B cells serve as the major reservoir for viral latency, and it is hypothesized that periodic reactivation from latently infected B cells contributes to maintaining long-term chronic infection. While fundamentally important to an understanding of GHV biology, aspects of B cell infection in latency establishment and maintenance are incompletely defined, especially roles for lytic replication and reactivation in this cell type. To address this knowledge gap and overcome limitations of replication-defective viruses, we generated a recombinant murine gammaherpesvirus 68 (MHV68) in which ORF50, the gene that encodes the essential immediate-early replication and transcription activator protein (RTA), was flanked by loxP sites to enable conditional ablation of lytic replication by ORF50 deletion in cells that express Cre recombinase. Following infection of mice that encode Cre in B cells with this virus, splenomegaly and viral reactivation from splenocytes were significantly reduced; however, the number of latently infected splenocytes was equivalent to WT MHV68. Despite ORF50 deletion, MHV68 latency was maintained over time in spleens of mice at levels approximating WT, reactivation-competent MHV68. Treatment of infected mice with lipopolysaccharide (LPS), which promotes B cell activation and MHV68 reactivation ex vivo, yielded equivalent increases in the number of latently infected cells for both ORF50-deleted and WT MHV68, even when mice were simultaneously treated with the antiviral drug cidofovir to prevent reactivation. Together, these data demonstrate that productive viral replication in B cells is not required for MHV68 latency establishment and support the hypothesis that B cell proliferation facilitates latency maintenance in vivo in the absence of reactivation. IMPORTANCE Gammaherpesviruses establish lifelong chronic infections in cells of the immune system and place infected hosts at risk for developing lymphomas and other diseases. It is hypothesized that gammaherpesviruses must initiate acute infection in these cells to establish and maintain long-term infection, but this has not been directly tested. We report here the use of a viral genetic system that allows for cell-type-specific deletion of a viral gene that is essential for replication and reactivation. We employ this system in an in vivo model to reveal that viral replication is not required to initiate or maintain infection within B cells.

The Contribution of Human Herpes Viruses to γδ T Cell Mobilisation in Co-Infections

γδ T cells are activated in viral, bacterial and parasitic infections. Among viruses that promote γδ T cell mobilisation in humans, herpes viruses (HHVs) occupy a particular place since they infect the majority of the human population and persist indefinitely in the organism in a latent state. Thus, other infections should, in most instances, be considered co-infections, and the reactivation of HHV is a serious confounding factor in attributing γδ T cell alterations to a particular pathogen in human diseases. We review here the literature data on γδ T cell mobilisation in HHV infections and co-infections, and discuss the possible contribution of HHVs to γδ alterations observed in various infectious settings. As multiple infections seemingly mobilise overlapping γδ subsets, we also address the concept of possible cross-protection.

Animal Models for Gammaherpesvirus Infections: Recent Development in the Analysis of Virus-Induced Pathogenesis

Epstein–Barr virus (EBV) is involved in the pathogenesis of various lymphomas and carcinomas, whereas Kaposi’s sarcoma-associated herpesvirus (KSHV) participates in the pathogenesis of endothelial sarcoma and lymphomas. EBV and KSHV are responsible for 120,000 and 44,000 annual new cases of cancer, respectively. Despite this clinical importance, no chemotherapies or vaccines have been developed for virus-specific treatment and prevention of these viruses. Humans are the only natural host for both EBV and KSHV, and only a limited species of laboratory animals are susceptible to their experimental infection; this strict host tropism has hampered the development of their animal models and thereby impeded the study of therapeutic and prophylactic strategies. To overcome this difficulty, three main approaches have been used to develop animal models for human gammaherpesvirus infections. The first is experimental infection of laboratory animals with EBV or KSHV. New-world non-human primates (NHPs) and rabbits have been mainly used in this approach. The second is experimental infection of laboratory animals with their own inherent gammaherpesviruses. NHPs and mice have been mainly used here. The third, a recent trend, employs experimental infection of EBV or KSHV or both to immunodeficient mice reconstituted with human immune system components (humanized mice). This review will discuss how these three approaches have been used to reproduce human clinical conditions associated with gammaherpesviruses and to analyze the mechanisms of their pathogenesis.

Murine γ-Herpesvirus 68 Induces Severe Lung Inflammation in IL-27-Deficient Mice with Liver Dysfunction Preventable by Oral Neomycin

IL-27 is an immunoregulatory cytokine consisting of p28 and EBI3. Its receptor also has two subunits, WSX1 and gp130. Although IL-27 promotes Th1 differentiation in naive T cells, it also induces IL-10 expression in effector Th1 cells to curtail excessive immune responses. By using p28-deficient mice and WSX1-deficient mice (collectively called IL-27-deficient mice), we examined the role of IL-27 in primary infection by murine γ-herpesvirus 68 (MHV68), a murine model of EBV. Upon airway infection with MHV68, IL-27-deficient mice had more aggravated lung inflammation than wild-type mice, although MHV68 infection per se was better controlled in IL-27-deficient mice. Although epithelial cells and alveolar macrophages were primarily infected by MHV68, interstitial macrophages and dendritic cells were the major producers of IL-27. The lung inflammation of IL-27-deficient mice was characterized by more IFN-γ-producing CD8+ T cells and fewer IL-10-producing CD8+ T cells than that of wild-type mice. An infectious mononucleosis-like disease was also aggravated in IL-27-deficient mice, with prominent splenomegaly and severe hepatitis. Infiltration of IFN-γ-producing effector cells and upregulation of the CXCR3 ligand chemokines CXCL9, CXCL10, and CXCL11 were noted in the liver of MHV68-infected mice. Oral neomycin effectively ameliorated hepatitis, with decreased production of these chemokines in the liver, suggesting that the intestinal microbiota plays a role in liver inflammation through upregulation of these chemokines. Collectively, IL-27 is essential for the generation of IL-10-producing effector cells in primary infection by MHV68. Our findings may also provide new insight into the mechanism of hepatitis associated with infectious mononucleosis.

Cross-species conservation of episome maintenance provides a basis for in vivo investigation of Kaposi's sarcoma herpesvirus LANA

Many pathogens, including Kaposi's sarcoma herpesvirus (KSHV), lack tractable small animal models. KSHV persists as a multi-copy, nuclear episome in latently infected cells. KSHV latency-associated nuclear antigen (kLANA) binds viral terminal repeat (kTR) DNA to mediate episome persistence. Model pathogen murine gammaherpesvirus 68 (MHV68) mLANA acts analogously on mTR DNA. kLANA and mLANA differ substantially in size and kTR and mTR show little sequence conservation. Here, we find kLANA and mLANA act reciprocally to mediate episome persistence of TR DNA. Further, kLANA rescued mLANA deficient MHV68, enabling a chimeric virus to establish latent infection in vivo in germinal center B cells. The level of chimeric virus in vivo latency was moderately reduced compared to WT infection, but WT or chimeric MHV68 infected cells had similar viral genome copy numbers as assessed by immunofluorescence of LANA intranuclear dots or qPCR. Thus, despite more than 60 Ma of evolutionary divergence, mLANA and kLANA act reciprocally on TR DNA, and kLANA functionally substitutes for mLANA, allowing kLANA investigation in vivo. Analogous chimeras may allow in vivo investigation of genes of other human pathogens.

Unsupervised learning techniques reveal heterogeneity in memory CD8+ T cell differentiation following acute, chronic and latent viral infections

CD8⁺ T lymphocytes are critical for the control of gammaherpesvirus latency. To determine how memory CD8⁺ T cells generated during latency differ from those primed during acute or chronic viral infection, we adoptively transferred naive P14 CD8⁺ T cells into uninfected recipients, and examined surface proteins, cytokines and transcription factors following infection with the Armstrong (acute) or Clone 13 (chronic) strains of lymphocytic choriomeningitis virus (LCMV), or murine gammaherpesvirus 68 (MHV68) expressing the LCMV epitope D^bGP33-41. By performing k-means clustering and generating self organizing maps (SOM), we observed increased short-lived effector-like, CD27^lo CD62L^lo and Bcl-6^lo CD8⁺ T cells following latent infection. In addition, we found that memory CD8⁺ T cells from latent primed mice underwent less expansion following adoptive transfer and antigen rechallenge. Data from cluster models were combined and visualized by principal component analysis (PCA) demonstrating memory CD8⁺ T cells from latent infection occupy an intermediate differentiation space.

A Murine Herpesvirus Closely Related to Ubiquitous Human Herpesviruses Causes T-Cell Depletion

The human roseoloviruses human herpesvirus 6A (HHV-6A), HHV-6B, and HHV-7 comprise the Roseolovirus genus of the human Betaherpesvirinae subfamily. Infections with these viruses have been implicated in many diseases; however, it has been challenging to establish infections with roseoloviruses as direct drivers of pathology, because they are nearly ubiquitous and display species-specific tropism. Furthermore, controlled study of infection has been hampered by the lack of experimental models, and until now, a mouse roseolovirus has not been identified. Herein we describe a virus that causes severe thymic necrosis in neonatal mice, characterized by a loss of CD4⁺ T cells. These phenotypes resemble those caused by the previously described mouse thymic virus (MTV), a putative herpesvirus that has not been molecularly characterized. By next-generation sequencing of infected tissue homogenates, we assembled a contiguous 174-kb genome sequence containing 128 unique predicted open reading frames (ORFs), many of which were most closely related to herpesvirus genes. Moreover, the structure of the virus genome and phylogenetic analysis of multiple genes strongly suggested that this virus is a betaherpesvirus more closely related to the roseoloviruses, HHV-6A, HHV-6B, and HHV-7, than to another murine betaherpesvirus, mouse cytomegalovirus (MCMV). As such, we have named this virus murine roseolovirus (MRV) because these data strongly suggest that MRV is a mouse homolog of HHV-6A, HHV-6B, and HHV-7.IMPORTANCE Herein we describe the complete genome sequence of a novel murine herpesvirus. By sequence and phylogenetic analyses, we show that it is a betaherpesvirus most closely related to the roseoloviruses, human herpesviruses 6A, 6B, and 7. These data combined with physiological similarities with human roseoloviruses collectively suggest that this virus is a murine roseolovirus (MRV), the first definitively described rodent roseolovirus, to our knowledge. Many biological and clinical ramifications of roseolovirus infection in humans have been hypothesized, but studies showing definitive causative relationships between infection and disease susceptibility are lacking. Here we show that MRV infects the thymus and causes T-cell depletion, suggesting that other roseoloviruses may have similar properties.

Murine Models of Epstein-Barr Virus-Associated Lymphomagenesis

The Epstein-Barr virus (EBV) is a B-lymphotropic gamma herpes virus associated with a number of malignancies. Most EBV-related cancers present complex medical management challenges; thus it has been essential to develop preclinical in vivo models allowing for the study of pathogenesis, prevention, and treatment of these diseases. Early in vivo models used nonhuman primates; however, such models were limited by the inability of EBV to achieve viral latency, availability, and cost. Immunodeficient mouse strains emerged as efficient models that allow for engraftment of human mononuclear cells and controlled evaluation of EBV-driven lymphoproliferative disease (EBV-LPD). By using highly immunodeficient strains of mice such as severe combined immune deficiency (SCID) and NOD/LtSz-scid ILrg(-/-)(NOG) mice, investigators have developed efficient platforms for evaluating pathogenesis of benign (HLH) and malignant (EBV-LPD) diseases associated with EBV. Humanized murine chimeric models have been essential tools for evaluating preventive strategies with vaccine and adoptive cellular approaches, as well as development of experimental therapeutic strategies. Manipulation of the human immune cells before engraftment or mutation of viral lytic and latent genes has enhanced our understanding of the oncogenic nature of EBV and the complexity of human immune responses to EBV. In this review, we discuss how the EBV murine models have evolved to become essential tools for studying the virology of EBV as it relates to human EBV-LPD pathogenesis, the immunobiology of innate and adaptive responses, and limitations of these models.

Interplay of Murine Gammaherpesvirus 68 with NF-kappaB Signaling of the Host

Herpesviruses establish a chronic infection in the host characterized by intervals of lytic replication, quiescent latency, and reactivation from latency. Murine gammaherpesvirus 68 (MHV68) naturally infects small rodents and has genetic and biologic parallels with the human gammaherpesviruses (gHVs), Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus. The murine gammaherpesvirus model pathogen system provides a platform to apply cutting-edge approaches to dissect the interplay of gammaherpesvirus and host determinants that enable colonization of the host, and that shape the latent or lytic fate of an infected cell. This knowledge is critical for the development of novel therapeutic interventions against the oncogenic gHVs. The nuclear factor kappa B (NF-κB) signaling pathway is well-known for its role in the promotion of inflammation and many aspects of B cell biology. Here, we review key aspects of the virus lifecycle in the host, with an emphasis on the route that the virus takes to gain access to the B cell latency reservoir. We highlight how the murine gammaherpesvirus requires components of the NF-κB signaling pathway to promote replication, latency establishment, and maintenance of latency. These studies emphasize the complexity of gammaherpesvirus interactions with NF-κB signaling components that direct innate and adaptive immune responses of the host. Importantly, multiple facets of NF-κB signaling have been identified that might be targeted to reduce the burden of gammaherpesvirus-associated diseases.

Latent virus infection upregulates CD40 expression facilitating enhanced autoimmunity in a model of multiple sclerosis

Epstein-Barr virus (EBV) has been identified as a putative environmental trigger of multiple sclerosis (MS) by multiple groups working worldwide. Previously, we reported that when experimental autoimmune encephalomyelitis (EAE) was induced in mice latently infected with murine γ-herpesvirus 68 (γHV-68), the murine homolog to EBV, a disease more reminiscent of MS developed. Specifically, MS-like lesions developed in the brain that included equal numbers of IFN-γ producing CD4⁺ and CD8⁺ T cells and demyelination, none of which is observed in MOG induced EAE. Herein, we demonstrate that this enhanced disease was dependent on the γHV-68 latent life cycle and was associated with STAT1 and CD40 upregulation on uninfected dendritic cells. Importantly, we also show that, during viral latency, the frequency of regulatory T cells is reduced via a CD40 dependent mechanism and this contributes towards a strong T helper 1 response that resolves in severe EAE disease pathology. Latent γ-herpesvirus infection established a long-lasting impact that enhances subsequent adaptive autoimmune responses.

Animal models of Epstein Barr virus infection

Epstein Barr virus (EBV) was the first human tumor virus to be identified. Despite 50years of research on this oncogenic virus, no therapeutic or prophylactic vaccine is available against this pathogen. In part, the development of such a vaccine is hampered by the lack of in vivo models for EBV infection and immune control. However, with the advent of mice with reconstituted human immune system components (HIS mice), certain aspects of EBV associated diseases and immune responses can be modeled in vivo. In this review, we will discuss the insights that can be gained from these experiments, and how immune system components can be manipulated to interrogate their function during EBV infection. Finally, we will compare EBV immunobiology in HIS mice to infection by EBV-related viruses in monkeys, and we will outline the strengths and weaknesses of these two in vivo models of EBV infection. Both of these models show great promise as a platform for preclinical EBV vaccine testing.

Antiherpesvirus activities of two novel 4'-thiothymidine derivatives, KAY-2-41 and KAH-39-149, are dependent on viral and cellular thymidine kinases

The emergence of drug-resistant herpesviruses represents a significant problem in clinical practice, primarily in immunocompromised patients. Furthermore, effective antiviral therapies against gammaherpesvirus-associated diseases are lacking. Here, we present two thiothymidine derivatives, KAY-2-41 and KAH-39-149, with different spectra of antiviral activity from those of the reference antiherpetic drugs, showing inhibitory activities against herpes simplex virus, varicella-zoster virus (VZV), and particularly against Epstein-Barr virus, with high selectivity in vitro. While KAY-2-41- and KAH-39-149-resistant herpesviruses were found to harbor mutations in the viral thymidine kinase (TK), these mutations conferred only low levels of resistance to these drugs but high levels to other TK-dependent drugs. Also, antiviral assays in HeLa TK-deficient cells showed a lack of KAY-2-41 and KAH-39-149 activities against herpes simplex virus 1 (HSV-1) and HSV-2 TK-deficient mutants. Furthermore, enzymatic TK assays showed the ability of HSV-1 TK, VZV TK, and cellular TK1 and TK2 to recognize and phosphorylate KAY-2-41 and KAH-39-149. These results demonstrate that the compounds depend on both viral and host TKs to exert antiviral activity. Additionally, the antiviral efficacy of KAH-39-149 proved to be superior to that of KAY-2-41 in a mouse model of gammaherpesvirus infection, highlighting the potential of this class of antiviral agents for further development as selective therapeutics against Epstein-Barr virus.

Environmental perturbation, inflammation and behavior in healthy and virus-infected mice

The development of so-called "sickness behaviors" (e.g., anorexia, anhedonia, reduced social interaction, fatigue) during infectious and inflammatory disease has been linked to facets of the immune response. Such problems can be particularly troublesome during chronic latent infection, as the host immune system must employ continual vigilance to maintain viral latency. Epstein-Barr virus (EBV) is a ubiquitous human gamma-herpesvirus that causes acute disease and establishes life-long latency in people. Murine gammaherpesvirus (MuGHV) is a natural pathogen of wild rodents that provides an experimental model for studying the pathophysiology of an EBV-like gamma-herpesvirus in mice. To evaluate this model with regard to sickness behavior and its exacerbation during a chronic latent viral disease, we exposed uninfected and MuGHV-infected C57BL/6J and BALB/cByJ mice to novel and potentially stressful environmental perturbations and measured the impact of these challenges on behavior and markers of inflammation. The data indicate that exposure of mice to environmental perturbations during the normal somnolent phase is associated with reduced activity during the subsequent active phase, despite an intervening rest period. Effects on inflammatory mediators were complex due to independent and interactive effects of infection status, mouse strain, and exposure to stressful environment. However, GCSF and MCP1 were consistently elevated in lung both immediately after and 12h after exposure to a "dirty" cage containing the resident mouse (DCR); this increase occurred in both C57BL/6J and BALB/cByJ mice and was independent of infection status. At 12h after DCR, IL1β and IP10 were also consistently elevated in lung. In response to DCR, BALB/cByJ mice showed a greater number of significant cytokine effects than did C57BL/6J mice. With regard to infection status, IP10 was consistently elevated in lung at both time points regardless of mouse strain or DCR exposure. Several analytes were affected by mouse strain in serum or lung at one or both time points, with most strain differences present in serum at E18. Taken together, the data show that exposure of mice to environmental perturbations is associated with systemic inflammation that is in part independent of genetic background or latent MuGHV infection and with reduced activity that could represent fatigue, depression, or other facets of sickness behavior.

Induction of encephalitis in rhesus monkeys infused with lymphocryptovirus-infected B-cells presenting MOG(34-56) peptide

The overlapping epidemiology of multiple sclerosis (MS) and Epstein-Barr virus (EBV), the increased risk to develop MS after infectious mononucleosis (IM) and the localization of EBV-infected B-cells within the MS brain suggest a causal link between EBV and MS. However, the underlying mechanism is unknown. We hypothesize that EBV-infected B-cells are capable of eliciting a central nervous system (CNS) targeting autoimmune reaction. To test this hypothesis we have developed a novel experimental model in rhesus monkeys of IM-like disease induced by infusing autologous B-lymphoblastoid cells (B-LCL). Herpesvirus papio (HVP) is a lymphocryptovirus related to EBV and was used to generate rhesus monkey B-LCL. Three groups of five animals were included; each group received three intravenous infusions of B-LCL that were either pulsed with the encephalitogenic self peptide MOG_34–56 (group A), a mimicry peptide (981–1003) of the major capsid protein of cytomegalovirus (CMVmcp_981–1003; group B) or the citrullinated MOG_34–56 (cMOG_34–56; group C). Groups A and B received on day 98 a single immunization with MOG_34–56 in incomplete Freund’s adjuvant (IFA). Group C monkeys were euthanized just prior to day 98 without booster immunization. We observed self-peptide-specific proliferation of T-cells, superimposed on similar strong proliferation of CD3⁺CD8⁺ T-cells against the B-LCL as observed in IM. The brains of several monkeys contained perivascular inflammatory lesions of variable size, comprising CD3⁺ and CD68⁺ cells. Moreover, clusters of CD3⁺ and CD20⁺ cells were detected in the meninges. The only evident clinical sign was substantial loss of bodyweight (>15%), a symptom observed both in early autoimmune encephalitis and IM. In conclusion, this model suggests that EBV-induced B-LCL can elicit a CNS targeting inflammatory (auto)immune reaction.

Heterologous immunity triggered by a single, latent virus in Mus musculus: combined costimulation- and adhesion- blockade decrease rejection

The mechanisms underlying latent-virus-mediated heterologous immunity, and subsequent transplant rejection, especially in the setting of T cell costimulation blockade, remain undetermined. To address this, we have utilized MHV68 to develop a rodent model of latent virus-induced heterologous alloimmunity. MHV68 infection was correlated with multimodal immune deviation, which included increased secretion of CXCL9 and CXCL10, and with the expansion of a CD8(dim) T cell population. CD8(dim) T cells exhibited decreased expression of multiple costimulation molecules and increased expression of two adhesion molecules, LFA-1 and VLA-4. In the setting of MHV68 latency, recipients demonstrated accelerated costimulation blockade-resistant rejection of skin allografts compared to non-infected animals (MST 13.5 d in infected animals vs 22 d in non-infected animals, p<.0001). In contrast, the duration of graft acceptance was equivalent between non-infected and infected animals when treated with combined anti-LFA-1/anti-VLA-4 adhesion blockade (MST 24 d for non-infected and 27 d for infected, p = n.s.). The combination of CTLA-4-Ig/anti-CD154-based costimulation blockade+anti-LFA-1/anti-VLA-4-based adhesion blockade led to prolonged graft acceptance in both non-infected and infected cohorts (MST>100 d for both, p<.0001 versus costimulation blockade for either). While in the non-infected cohort, either CTLA-4-Ig or anti-CD154 alone could effectively pair with adhesion blockade to prolong allograft acceptance, in infected animals, the prolonged acceptance of skin grafts could only be recapitulated when anti-LFA-1 and anti-VLA-4 antibodies were combined with anti-CD154 (without CTLA-4-Ig, MST>100 d). Graft acceptance was significantly impaired when CTLA-4-Ig alone (no anti-CD154) was combined with adhesion blockade (MST 41 d). These results suggest that in the setting of MHV68 infection, synergy occurs predominantly between adhesion pathways and CD154-based costimulation, and that combined targeting of both pathways may be required to overcome the increased risk of rejection that occurs in the setting of latent-virus-mediated immune deviation.

Humanized mouse models of epstein-barr virus infection and associated diseases

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus infecting more than 90% of the adult population of the world. EBV is associated with a variety of diseases including infectious mononucleosis, lymphoproliferative diseases, malignancies such as Burkitt lymphoma and nasopharyngeal carcinoma, and autoimmune diseases including rheumatoid arthritis (RA). EBV in nature infects only humans, but in an experimental setting, a limited species of new-world monkeys can be infected with the virus. Small animal models, suitable for evaluation of novel therapeutics and vaccines, have not been available. Humanized mice, defined here as mice harboring functioning human immune system components, are easily infected with EBV that targets cells of the hematoimmune system. Furthermore, humanized mice can mount both cellular and humoral immune responses to EBV. Thus, many aspects of human EBV infection, including associated diseases (e.g., lymphoproliferative disease, hemophagocytic lymphohistiocytosis and erosive arthritis resembling RA), latent infection, and T-cell-mediated and humoral immune responses have been successfully reproduced in humanized mice. Here we summarize recent achievements in the field of humanized mouse models of EBV infection and show how they have been utilized to analyze EBV pathogenesis and normal and aberrant human immune responses to the virus.

Systemic and local infection routes govern different cellular dissemination pathways during gammaherpesvirus infection in vivo

Human gammaherpesviruses cause morbidity and mortality associated with infection and transformation of lymphoid and endothelial cells. Knowledge of cell types involved in virus dissemination from primary virus entry to virus latency is fundamental for the understanding of gammaherpesvirus pathogenesis. However, the inability to directly trace cell types with respect to virus dissemination pathways has prevented definitive conclusions regarding the relative contribution of individual cell types. Here, we describe that the route of infection affects gammaherpesvirus dissemination pathways. We constructed a recombinant murine gammaherpesvirus 68 (MHV-68) variant harboring a cassette which switches fluorescent markers in a Cre-dependent manner. Since the recombinant virus which was constructed on the wild-type background was attenuated, in this study we used an M1-deleted version, which infected mice with normal kinetics. Infection of Cre-transgenic mice with this convertible virus was used to estimate the quantitative contribution of defined cell types to virus productivity and dissemination during the acute phase of MHV-68 infection. In systemic infection, we found splenic vascular endothelial cells (EC) among the first and main cells to produce virus. After local infection, the contribution of EC to splenic virus production did not represent such early kinetics. However, at later time points, B cell-derived viruses dominated splenic productivity independently of systemic or local infection. Systemic versus local infection also governed the cell types involved in loading peritoneal exudate cells, leading to latency in F4/80- and CD11b-positive target cells. Systemic infection supported EC-driven dissemination, whereas local infection supported B cell-driven dissemination.

Activity and mechanism of action of HDVD, a novel pyrimidine nucleoside derivative with high levels of selectivity and potency against gammaherpesviruses

A novel nucleoside analogue, 1-[(2S,4S-2-(hydroxymethyl)-1,3-dioxolan-4-yl]5-vinylpyrimidine-2,4(1H,3H)-dione, or HDVD, was evaluated against a wide variety of herpesviruses and was found to be a highly selective inhibitor of replication of the gammaherpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV). HDVD had also a pronounced inhibitory activity against murine herpesvirus 68 (MHV-68) and herpes simplex virus 1 (HSV-1). In contrast, replication of herpesvirus saimiri (HVS), HSV-2, and varicella-zoster virus (VZV) was weakly inhibited by the compound, and no antiviral activity was determined against human cytomegalovirus (HCMV) and rhesus rhadinovirus (RRV). The HDVD-resistant virus phenotype contained point mutations in the viral thymidine kinase (TK) of HSV-1, MHV-68, and HVS isolates. These mutations conferred cross-resistance to other TK-dependent drugs, with the exception of an MHV-68 mutant (E358D) that exhibited resistance only to HDVD. HSV-1 and HVS TK-mutants isolated under selective pressure with bromovinyldeoxyuridine (BVDU) also showed reduced sensitivity to HDVD. Oral treatment with HDVD and BVDU was assessed in an intranasal model of MHV-68 infection in BALB/c mice. In contrast to BVDU treatment, HDVD-treated animals showed a reduction in viral DNA loads and diminished viral gene expression during acute viral replication in the lungs in comparison to levels in untreated controls. The valyl ester prodrug of HDVD (USS-02-71-44) suppressed the latent infection in the spleen to a greater extent than HDVD. In the present study, HDVD emerged as a highly potent antiviral with a unique spectrum of activity against herpesviruses, in particular, gammaherpesviruses, and may be of interest in the treatment of virus-associated diseases.

A heparan-dependent herpesvirus targets the olfactory neuroepithelium for host entry

Herpesviruses are ubiquitous pathogens that cause much disease. The difficulty of clearing their established infections makes host entry an important target for control. However, while herpesviruses have been studied extensively in vitro, how they cross differentiated mucus-covered epithelia in vivo is unclear. To establish general principles we tracked host entry by Murid Herpesvirus-4 (MuHV-4), a lymphotropic rhadinovirus related to the Kaposi's Sarcoma-associated Herpesvirus. Spontaneously acquired virions targeted the olfactory neuroepithelium. Like many herpesviruses, MuHV-4 binds to heparan sulfate (HS), and virions unable to bind HS showed poor host entry. While the respiratory epithelium expressed only basolateral HS and was bound poorly by incoming virions, the neuroepithelium also displayed HS on its apical neuronal cilia and was bound strongly. Incoming virions tracked down the neuronal cilia, and either infected neurons or reached the underlying microvilli of the adjacent glial (sustentacular) cells and infected them. Thus the olfactory neuroepithelium provides an important and complex site of HS-dependent herpesvirus uptake.

Herpesviruses are supremely successful mammalian parasites. Yet their infections rarely present until well established, so how new hosts are first infected has been unclear. Understanding this is likely to be crucial for infection control. Using Murid Herpesvirus-4, a relative of the Kaposi's Sarcoma-associated Herpesvirus, we identified the olfactory neuroepithelium as a major portal of host entry. Heparan sulfate (HS) binding, which is common to many herpesviruses, played a key role. The HS of most epithelia is solely basolateral and therefore inaccessible to incoming, apical virions. The neuroepithelium, by contrast, also displayed HS on its apical surface. This comprises a dense meshwork of the neuronal cilia that mediate olfaction. Incoming virions bound to the cilia, as did a recombinant form of the virion glycoprotein H/L heterodimer. Some virions tracked down the cilia to infect neurons. Others were transferred to the microvilli of adjacent sustentacular cells. The central role of HS in this first detailed description of host entry by a mammalian herpesvirus, and the paucity of accessible HS on other epithelia, suggested that many HS-binding herpesviruses could follow a similar path.

Myeloid infection links epithelial and B cell tropisms of Murid Herpesvirus-4

Gamma-herpesviruses persist in lymphocytes and cause disease by driving their proliferation. Lymphocyte infection is therefore a key pathogenetic event. Murid Herpesvirus-4 (MuHV-4) is a rhadinovirus that like the related Kaposi's Sarcoma-associated Herpesvirus persists in B cells in vivo yet infects them poorly in vitro. Here we used MuHV-4 to understand how virion tropism sets the path to lymphocyte colonization. Virions that were highly infectious in vivo showed a severe post-binding block to B cell infection. Host entry was accordingly an epithelial infection and B cell infection a secondary event. Macrophage infection by cell-free virions was also poor, but improved markedly when virion binding improved or when macrophages were co-cultured with infected fibroblasts. Under the same conditions B cell infection remained poor; it improved only when virions came from macrophages. This reflected better cell penetration and correlated with antigenic changes in the virion fusion complex. Macrophages were seen to contact acutely infected epithelial cells, and cre/lox-based virus tagging showed that almost all the virus recovered from lymphoid tissue had passed through lysM⁺ and CD11c⁺ myeloid cells. Thus MuHV-4 reached B cells in 3 distinct stages: incoming virions infected epithelial cells; infection then passed to myeloid cells; glycoprotein changes then allowed B cell infection. These data identify new complexity in rhadinovirus infection and potentially also new vulnerability to intervention.

Rhadinoviruses cause lymphocytic cancers. Their infection of lymphocytes is therefore an important therapeutic target. How this occurs is unclear. One prevalent hypothesis has been that virions directly infect lymphocytes when they enter new hosts. Here we show that host entry by Murid Herpesvirus-4, a close relative of the Kaposi's Sarcoma-associated Herpesvirus, is an epithelial rather than a lymphocyte infection: the mucosal lymphoid colonization typical of acute infectious mononucleosis only occurred later. Macrophages were closely associated with the acutely infected epithelium, and most if not all of the virus reaching B cells showed evidence of previous myeloid cell infection. Macrophage-derived virions showed a greatly enhanced capacity for lymphocyte infection that was associated with antigenic changes in the viral fusion proteins. Thus host colonization required epithelial and myeloid infections before there was lymphocyte infection. The implication is that each of these infection events could be independently targeted to limit viral persistence.

Murine gammaherpesvirus 68 LANA acts on terminal repeat DNA to mediate episome persistence

Murine gammaherpesvirus 68 (MHV68) ORF73 (mLANA) has sequence homology to Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA). LANA acts on the KSHV terminal repeat (TR) elements to mediate KSHV episome maintenance. Disruption of mLANA expression severely reduces the ability of MHV68 to establish latent infection in mice, consistent with the possibility that mLANA mediates episome persistence. Here we assess the roles of mLANA and MHV68 TR (mTR) elements in episome persistence. mTR-associated DNA persisted as an episome in latently MHV68-infected tumor cells, demonstrating that the mTR elements can serve as a cis-acting element for MHV68 episome maintenance. In some cases, both control vector and mTR-associated DNAs integrated into MHV68 episomal genomes. Therefore, we also assessed the roles of mTRs as well as mLANA in the absence of infection. DNA containing both mLANA and mTRs in cis persisted as an episome in murine A20 or MEF cells. In contrast, mTR DNA never persisted as an episome in the absence of mLANA. mLANA levels were increased when mLANA was expressed from its native promoters, and episome maintenance was more efficient with higher mLANA levels. Increased numbers of mTRs conferred more efficient episome maintenance, since DNA containing mLANA and eight mTR elements persisted more efficiently in A20 cells than did DNA with mLANA and two or four mTRs. Similar to KSHV LANA, mLANA broadly associated with mitotic chromosomes but relocalized to concentrated dots in the presence of episomes. Therefore, mLANA acts on mTR elements to mediate MHV68 episome persistence.

Gammaherpesvirus latency accentuates EAE pathogenesis: relevance to Epstein-Barr virus and multiple sclerosis

Epstein-Barr virus (EBV) has been identified as a putative environmental trigger of multiple sclerosis (MS), yet EBV's role in MS remains elusive. We utilized murine gamma herpesvirus 68 (γHV-68), the murine homolog to EBV, to examine how infection by a virus like EBV could enhance CNS autoimmunity. Mice latently infected with γHV-68 developed more severe EAE including heightened paralysis and mortality. Similar to MS, γHV-68EAE mice developed lesions composed of CD4 and CD8 T cells, macrophages and loss of myelin in the brain and spinal cord. Further, T cells from the CNS of γHV-68 EAE mice were primarily Th1, producing heightened levels of IFN-γ and T-bet accompanied by IL-17 suppression, whereas a Th17 response was observed in uninfected EAE mice. Clearly, γHV-68 latency polarizes the adaptive immune response, directs a heightened CNS pathology following EAE induction reminiscent of human MS and portrays a novel mechanism by which EBV likely influences MS and other autoimmune diseases.

CD8(+) T cells from mice transnuclear for a TCR that recognizes a single H-2K(b)-restricted MHV68 epitope derived from gB-ORF8 help control infection

To study the CD8(+) T cell response against a mouse γ-herpes virus, we generated K(b)-MHV-68-ORF8(604-612)RAG(-/-) CD8(+) T cell receptor transnuclear (TN) mice as a source of virus-specific CD8(+) T cells. K(b)-ORF8-Tet(+) CD8(+) T cells, expanded in the course of a resolving MHV-68 infection, served as a source of nucleus donors. Various in vivo and ex vivo assay criteria demonstrated the fine specificity and functionality of TN cells. TN cells proliferated extensively in response to viral infection, helped control viral burden, and exhibited a phenotype similar to that of endogenous K(b)-ORF8-Tet(+) cells. When compared to OT-1 cells, TN cells displayed distinct properties in response to lymphopenia and cognate antigen stimulation, which may be attributable to the affinity of the TCR expressed by the TN cells. The availability of MHV-68-specific CD8(+) TCR TN mice provides a new tool for investigating aspects of host-pathogen interactions unique to γ-herpes viruses.

Murine gammaherpesvirus 68 infection protects lupus-prone mice from the development of autoimmunity

Gammaherpesvirus infections, such as those caused by EBV, have been suggested to promote the development of autoimmunity. To test this idea, we infected healthy WT and lupus-prone B6.Sle123 mice with an EBV-related and rodent-specific gammaherpesvirus, γHV68. Although acute γHV68 infection increased autoantibody levels for 4 to 6 wk, latent infection inhibited these responses for 1 y. The inhibition of autoantibody expression was only observed in B6.Sle123 females and not in males, which already displayed lower autoantibody titers. Contrary to the initial hypothesis, infection of young B6.Sle123 mice, both male and female, resulted in suppression of lymphoid activation and expansion and of glomerular inflammation and sclerosis, preserving kidney function. Moreover, γHV68 infection led to reduced autoantibody titers, lymphoid activation, and glomerular inflammation whether lupus-prone females were infected before or during disease manifestation. Finally, γHV68 infection also inhibited autoantibody production in the genetically distinct MRL/lpr lupus-prone mice. Our findings indicate that γHV68 infection strongly inhibits the development and progression of lupus-like disease in mice that spontaneously develop this condition mediating its beneficial effects at the humoral, cellular, and organ levels. The mechanisms by which the virus exerts this down-modulatory action are not yet clear, but appear to operate via reduced activation of dendritic cells, T cells, and B cells. Gammaherpesviruses coevolved with the vertebrate immune systems, establishing lifelong infections in humans and other mammals. Our findings that γHV68 infection prevents rather than exacerbates autoimmunity in mice suggest that infection with gammaherpesviruses may be protective rather than pathological in most individuals.

Viral Infections of Laboratory Mice

Viral infections of laboratory mice have considerable impact on research results, and prevention of such infections is therefore of crucial importance. This chapter covers infections of mice with the following viruses: herpesviruses, mousepox virus, murine adenoviruses, polyomaviruses, parvoviruses, lactate dehydrogenase-elevating virus, lymphocytic choriomeningitis virus, mammalian orthoreovirus serotype 3, murine hepatitis virus, murine norovirus, murine pneumonia virus, murine rotavirus, Sendai virus, and Theiler’s murine encephalomyelitis virus. For each virus, there is a description of the agent, epizootiology, clinical symptoms, pathology, methods of diagnosis and control, and its impact on research.

A role for DNA-dependent activator of interferon regulatory factor in the recognition of herpes simplex virus type 1 by glial cells

BACKGROUND

The rapid onset of potentially lethal neuroinflammation is a defining feature of viral encephalitis. Microglia and astrocytes are likely to play a significant role in viral encephalitis pathophysiology as they are ideally positioned to respond to invading central nervous system (CNS) pathogens by producing key inflammatory mediators. Recently, DNA-dependent activator of IFN regulatory factor (DAI) has been reported to function as an intracellular sensor for DNA viruses. To date, the expression and functional role of DAI in the inflammatory responses of resident CNS cells to neurotropic DNA viruses has not been reported.

METHODS

Expression of DAI and its downstream effector molecules was determined in C57BL/6-derived microglia and astrocytes, either at rest or following exposure to herpes simplex virus type 1 (HSV-1) and/or murine gammaherpesvirus-68 (MHV-68), by immunoblot analysis. In addition, such expression was studied in ex vivo microglia/macrophages and astrocytes from uninfected animals or mice infected with HSV-1. Inflammatory cytokine production by glial cultures following transfection with a DAI specific ligand (B-DNA), or following HSV-1 challenge in the absence or presence of siRNA directed against DAI, was assessed by specific capture ELISA. The production of soluble neurotoxic mediators by HSV-1 infected glia following DAI knockdown was assessed by analysis of the susceptibility of neuron-like cells to conditioned glial media.

RESULTS

We show that isolated microglia and astrocytes constitutively express DAI and its effector molecules, and show that such expression is upregulated following DNA virus challenge. We demonstrate that these resident CNS cells express DAI in situ, and show that its expression is similarly elevated in a murine model of HSV-1 encephalitis. Importantly, we show B-DNA transfection can elicit inflammatory cytokine production by isolated glial cells and DAI knockdown can significantly reduce microglial and astrocyte responses to HSV-1. Finally, we demonstrate that HSV-1 challenged microglia and astrocytes release neurotoxic mediators and show that such production is significantly attenuated following DAI knockdown.

CONCLUSIONS

The functional expression of DAI by microglia and astrocytes may represent an important innate immune mechanism underlying the rapid and potentially lethal inflammation associated with neurotropic DNA virus infection.

SLAM family receptors and SAP adaptors in immunity

The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia. SAP consists almost entirely of a single SH2 protein domain that interacts with the cytoplasmic tail of SLAM and related receptors, including 2B4, Ly108, CD84, Ly9, and potentially CRACC. SLAM family members are now recognized as important immunomodulatory receptors with roles in cytotoxicity, humoral immunity, autoimmunity, cell survival, lymphocyte development, and cell adhesion. In this review, we cover recent findings on the roles of SLAM family receptors and the SAP family of adaptors, with a focus on their regulation of the pathways involved in the pathogenesis of XLP and other immune disorders.

Sleep and fatigue in mice infected with murine gammaherpesvirus 68

Fatigue, a common symptom of many acute and chronic medical conditions, reduces both quality of life and workplace productivity and can be disabling. However, the pathophysiologic mechanisms that underlie fatigue can be difficult to study in human populations due to the patient heterogeneity, the variety of underlying causes and potential triggering events, and an inability to collect samples that may be essential to elucidation of mechanisms (e.g., brain). Although the etiology of chronic fatigue syndrome (CFS) remains elusive, some studies have implicated viral infections, including Epstein-Barr virus (EBV), a human gammaherpesvirus, as a potential factor in the pathogenesis of CFS. Murine gammaherpesvirus 68 (γHV68) is a mouse pathogen that shares many similarities with human γHVs, including EBV. In this study, we use γHV68-infected C57BL/6J mice as a model system for studying the impact of chronic viral infection on sleep-wake behavior, activity patterns, and body temperature profiles. Our data show that γHV68 alters sleep, activity, and temperature in a manner suggestive of fatigue. In mice infected with the highest dose used in this study (40,000plaque forming units), food intake, body weight, wheel running, body temperature, and sleep were normal until approximately 7days after infection. These parameters were significantly altered during days 7 through 11, returned to baseline levels at day 12 after infection, and remained within the normal range for the remainder of the 30-day period after inoculation. At that time, both infected and uninfected mice were injected with lipopolysaccharide (LPS), and their responses monitored. Uninfected mice given LPS developed a modest and transient febrile response during the initial light phase (hours 12 through 24) after injection. In contrast, infected mice developed changes in core body temperatures that persisted for at least 5days. Infected mice showed an initial hypothermia that lasted for approximately 12h, followed by a modest fever that persisted for several hours. For the remainder of the 5-day recording period, they showed mild hypothermia during the dark phase. Running wheel activity of infected mice was reduced for at least 5days after injection of LPS, but for only 12h in uninfected mice. Collectively, these observations indicate that (1) physiologic and behavioral processes in mice are altered and recover during an early phase of infection, and (2) mice with latent γHV68 infection have an exacerbated response to challenge with LPS. These findings indicate that laboratory mice with γHV68 infections may provide a useful model for the study of fatigue and other physiologic and behavioral perturbations that may occur during acute and chronic infection with gammaherpesviruses.

KSHV infects a subset of human tonsillar B cells, driving proliferation and plasmablast differentiation

Kaposi sarcoma-associated herpesvirus (KSHV; also known as HHV8) is the causative agent of two B cell tumors, multicentric Castleman disease (MCD) and primary effusion lymphoma (PEL). However, little is known about the nature of the specific B cell subtype(s) most susceptible to infection. Identifying these cells would provide direct insight into KSHV transmission and virus-induced transformation. To identify this subset and to determine whether infection alters its cellular phenotype, we exposed human tonsillar cells to KSHV and characterized infected cells using high-throughput multispectral imaging flow cytometry (MIFC). Stable expression of the virally encoded latency-associated nuclear antigen (LANA), a marker of latent KSHV infection, was observed predominantly in cells expressing the l light chain of the B cell receptor. These LANA+ B cells proliferated and exhibited similarities to the cells characteristic of MCD (IgMl-expressing plasmablasts), including blasting morphology with elevated expression of Ki67, variable expression of CD27, and high levels of IgM and IL-6 receptor. Furthermore, the proportion of infected cells showing a blasting phenotype increased upon addition of exogenous IL-6. Our data lead us to propose that oral transmission of KSHV involves the latent infection of a subset of tonsillar IgMl-expressing B cells, which then proliferate as they acquire the plasmablast phenotype characteristic of MCD.

Mononucleosis and antigen-driven T cell responses have different requirements for interleukin-2 signaling in murine gammaherpesvirus infection

Interleukin-2 (IL-2) has been implicated as being necessary for the optimal formation of primary CD8(+) T cell responses against various pathogens. Here we have examined the role that IL-2 signaling plays in several aspects of a CD8(+) T cell response against murine gammaherpesvirus 68 (MHV-68). Exposure to MHV-68 causes a persistent infection, along with infectious mononucleosis, providing a model for studying these processes in mice. Our study indicates that CD25 is necessary for optimal expansion of the antigen-specific CD8(+) T cell response but not for the long-term memory response. Contrastingly, IL-2 signaling through CD25 is absolutely required for CD8(+) T cell mononucleosis.

Identification and analysis of expression of novel microRNAs of murine gammaherpesvirus 68

Murine gammaherpesvirus 68 (MHV-68) is closely related to Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) and provides a small-animal model with which to study the pathogenesis of gammaherpesvirus (gammaHV) infections. To completely explore the potential of the MHV-68 system for the investigation of gammaHV microRNAs (miRNAs), it would be desirable to know the number and expression patterns of all miRNAs encoded by MHV-68. By deep sequencing of small RNAs, we systematically investigated the expression profiles of MHV-68 miRNAs in both lytically and persistently infected cells. In addition to the nine known MHV-68 miRNAs, we identified six novel MHV-68 miRNA genes and analyzed the expression levels of all MHV-68 miRNAs. Furthermore, we also characterized the cellular miRNA expression signatures in MHV-68-infected versus noninfected NIH 3T3 fibroblasts and in 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-treated versus nontreated S11 cells. We found that mmu-mir-15b and mmu-mir-16 are highly upregulated upon MHV-68 infection of NIH 3T3 cells, indicating a potential role for cellular miRNAs during MHV-68 infection. Our data will aid in the full exploration of the functions of gammaHV miRNAs.

Chemokine receptor CCR7 contributes to a rapid and efficient clearance of lytic murine gamma-herpes virus 68 from the lung, whereas bronchus-associated lymphoid tissue harbors virus during latency

Murine gamma-herpes virus 68 is a natural rodent pathogen closely related to the human gamma-herpes viruses Kaposi's sarcoma-associated herpes virus and EBV. By intranasally infecting wild-type and CCR7-deficient mice, we investigated whether CCR7 is necessary for viral clearance from the lung and the establishment of latency. We found during the lytic phase of infection that inflammation in lungs of CCR7(-/-) mice was more severe and viral load significantly higher compared with wild-type littermates. In addition, activation of T cells was delayed and clearance of the inflammation was retarded in mutant lungs, demonstrating that CCR7 is necessary for a rapid and efficient immune response. However, for the establishment of splenomegaly and latency, the presence of CCR7 was dispensable. Finally, by microdissecting BALT, we could demonstrate that these ectopic lymphoid structures are a place in the lung where virus resides during latency.

The M10 locus of murine gammaherpesvirus 68 contributes to both the lytic and the latent phases of infection

Murine gammaherpesvirus 68 (MHV-68) is closely related to Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus (KSHV) and provides a small-animal model to study the pathogenesis of gammaherpesvirus (gammaHV) infections. According to the colinear organization of the gammaHV genomes, the M10 locus is situated at a position equivalent to the K12 locus of KSHV, which codes for proteins of the kaposin family. The M10 locus of MHV-68 has been predicted to code for three overlapping open reading frames (M10a, M10b, and M10c [M10a-c]) with unknown function. In addition, the M10 locus contains a lytic origin of replication (oriLyt). To elucidate the function of the M10 locus during lytic and latent infections, we investigated, both in vitro and in vivo, the following four recombinant viruses which were generated using MHV-68 cloned as a bacterial artificial chromosome: (i) a mutant virus with a deletion which affects both the coding region for M10a-c and the oriLyt; (ii) a revertant virus in which both the M10a-c coding region and the oriLyt were reverted to those of the wild type; (iii) a virus with an ectopic insertion of the oriLyt, which restores the function of the oriLyt but not the M10a-c coding region; and (iv) a mutant virus with a deletion in the oriLyt only. While the mutants were slightly attenuated with regard to lytic replication in cell culture, they showed severe growth defects in vivo. Both lytic replication and latency amplification were strongly reduced. In contrast, both the revertant virus and the virus with the ectopic oriLyt insertion grew very similarly to the parental wild-type virus both in vitro and in vivo. Thus, we provide genetic evidence that mutation of the oriLyt, and not of putative protein coding sequences within the M10a-c region, is responsible for the observed phenotype. We conclude that the oriLyt in the M10 locus plays an important role during infection of mice with MHV-68.

Disruption of murine cardiac allograft acceptance by latent cytomegalovirus

Cytomegalovirus (CMV) reactivation is a well-described complication of solid organ transplantation. These studies were performed to (1) determine if cardiac allograft transplantation of latently infected recipients results in reactivation of CMV and (2) determine what impact CMV might have on development of graft acceptance/tolerance. BALB/c cardiac allografts were transplanted into C57BL/6 mice with/without latent murine CMV (MCMV). Recipients were treated with gallium nitrate induction and monitored for graft survival, viral immunity and donor reactive DTH responses. Latently infected allograft recipients had approximately 80% graft loss by 100 days after transplant, compared with approximately 8% graft loss in naïve recipients. PCR evaluation demonstrated that MCMV was transmitted to cardiac grafts in all latently infected recipients, and 4/8 allografts had active viral transcription compared to 0/6 isografts. Latently infected allograft recipients showed intragraft IFN-alpha expression consistent with MCMV reactivation, but MCMV did not appear to negatively influence regulatory gene expression. Infected allograft recipients had disruption of splenocyte DTH regulation, but recipient splenocytes remained unresponsive to donor antigen even after allograft losses. These data suggest that transplantation in an environment of latent CMV infection may reactivate virus, and that intragraft responses disrupt development of allograft acceptance.

Identification of closely spaced but distinct transcription initiation sites for the murine gammaherpesvirus 68 latency-associated M2 gene

Murine gammaherpesvirus 68 (MHV68) infection of mice provides a tractable small-animal system for assessing viral requirements for establishment of and reactivation from latency. The M2 gene product has no homology to any known proteins but has been shown to play a role in both the establishment of MHV68 latency and reactivation from latency. Furthermore, we have recently shown that M2 expression in primary murine B cells leads to enhanced proliferation, survival, and differentiation toward a preplasma memory B-cell phenotype (A. M. Siegel, J. H. Herskowitz, and S. H. Speck, PLoS Pathog. 4:e1000039, 2008). Previous studies have characterized the structure of the M2 transcript, but to date there has been no characterization of the M2 promoter, additional open reading frames (ORFs) in the M2 region, or identified splice acceptor and splice donor sites present in the previously characterized M2 gene transcript. Here we report (i) the identification and disruption of a novel transcript that encodes a short, previously unreported ORF (M2b) located in the intron between exon 1 and exon 2 of the M2 transcript; (ii) the identification of clustered but distinct M2 gene transcription initiation sites suggesting the presence of multiple promoters involved in regulating M2 gene transcription; (iii) the characterization in vivo of recombinant MHV68 harboring deletions within the identified M2 promoter region; and (iv) the in vivo analysis of recombinant MHV68 harboring mutations that ablate either the identified M2 splice acceptor or splice donor site. Finally, our 5' rapid amplification of cDNA ends in conjunction with splice acceptor mutation analyses confirmed that all detected M2 gene transcripts expressed during MHV68 infection in mice splice into the M2 ORF downstream of the first AUG codon, providing strong evidence that initiation of the M2 gene product arises from the second AUG codon located at residue 8 in the M2 ORF. This initial detailed analysis of M2 gene transcription in vivo will aid future studies on regulation of M2 gene expression.

TLR9 contributes to antiviral immunity during gammaherpesvirus infection

The human gammaherpesviruses Kaposi's sarcoma-associated herpesvirus and EBV cause important infections. As pathogenetic studies of the human infections are restricted, murine gammaherpesvirus 68 serves as a model to study gammaherpesvirus pathogenesis. TLRs are a conserved family of receptors detecting microbial molecular patterns. Among the TLRs, TLR9 recognizes unmethylated CpG DNA motifs present in bacterial and viral DNA. The aim of this study was to assess the role of TLR9 in gammaherpesvirus pathogenesis. Upon stimulation with murine gammaherpesvirus 68, Flt3L-cultured bone marrow cells (dendritic cells) from TLR9-/- mice secreted reduced levels of IL-12, IFN-alpha, and IL-6, when compared with dendritic cells from wild-type mice. Intranasal infection of TLR9-/- and wild-type mice did not reveal any differences during lytic and latent infection. In contrast, when infected i.p., TLR9-/- mice showed markedly higher viral loads both during lytic and latent infection. Thus, we show for the first time that TLR9 is involved in gammaherpesvirus pathogenesis and contributes to organ-specific immunity.

Epstein-Barr virus: a paradigm for persistent infection - for real and in virtual reality

The really interesting thing about herpesviruses is that they can establish lifelong persistant infections in immunocompetent hosts. At first glance, they would seem to have very different ways of doing this. Here we will use as a model our current understanding of how the human herpesvirus Epstein-Barr virus establishes and maintains such an infection. We apply information from a wide range of sources including laboratory experimentation, clinical observation, animal models and a new computer simulation. We propose that the detailed mechanisms for establishing infection are dependent on the virus and tissues involved, but the strategy is the same - to persist in a long-lived cell type where the virus is invisible to the immune system and nonpathogenic.

Proteins of the secretory pathway govern virus productivity during lytic gammaherpesvirus infection

Background: Diseases caused by gammaherpesviruses continue to be a challenge for human health and antiviral treatment. Most of the commonly used antiviral drugs are directed against viral gene products. However, the emergence of drug-resistant mutations ma limit the effectiveness of these drugs. Since viruses require a host cell to propagate, the search for host cell targets is an interestin alternative. Methods: In this study, we infected three different cell types (fibroblasts, endothelial precursor cells and macrophages with a murine gammaherpesvirus and analysed the host cell response for changes either common to all or unique to a particular cell type using oligonucleotide microarrays. Results: The analysis revealed a number of genes whose transcription was significantly up- or down-regulated in either one or two of the cell types tested. After infection, only two genes, Lman1 (also known as ERGIC53) an synaptobrevin-like 1 (sybl1) were significantly up-regulated in all three cell types, suggestive for a general role for the virus life cycl independent of the cell type. Both proteins have been implicated in cellular exocytosis and transport of glycoproteins through the secre tory pathway. To test the significance of the observed up-regulation, the functionality of these proteins was modulated, and the effect on virus replication was monitored. Inhibition of either Lman1 or sybl1 resulted in a significant reduction in virus production. Conclusions: This suggests that proteins of the secretory pathway which appear to be rate limiting for virus production may represent new targets for intervention.

Exacerbation of established pulmonary fibrosis in a murine model by gammaherpesvirus

RATIONALE

Idiopathic pulmonary fibrosis is a progressive disease with high mortality. Although most patients have a slow, progressive course, some patients will have an acute deterioration in function or acute exacerbation, which carries a poor prognosis. In some cases, acute deterioration is associated with infection. Herpesviruses have been associated with this disease. Fibrocytes have also been shown to be important in the pathogenesis of pulmonary fibrosis.

OBJECTIVES

To develop a murine model for infectious exacerbation of preexisting fibrosis, and provide mechanistic insight into the role of herpesviruses in fibrotic disease.

METHODS

We used a model of fluorescein isothiocyanate-induced pulmonary fibrosis in mice. Infection with a murine gammaherpesvirus was given at time of established lung fibrosis. Measurements were made at the time of peak lytic viral replication.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that infection with gammaherpesvirus can exacerbate established fluorescein isothiocyanate-induced fibrosis evidenced by increased total lung collagen, histologic changes of acute lung injury, and diminished lung function. Gammaherpesvirus can exacerbate preexisting fibrosis in a Th1 cytokine environment and in the absence of Th2 cytokines. Gammaherpesvirus increases fibrocyte recruitment to the lung in wild-type, but not CCR2(-/-) mice, in part because viral infection up-regulates production of CCL2 and CCL12, chemokines important for fibrocyte recruitment. In contrast, mouse adenovirus infection did not exacerbate collagen deposition.

CONCLUSIONS

These data provide a new model for gammaherpesvirus exacerbation of established pulmonary fibrosis. The up-regulation of chemokines during viral infection and subsequent recruitment of fibrocytes to the lung likely contribute to augmentation of pulmonary fibrosis.

IgG fc receptors provide an alternative infection route for murine gamma-herpesvirus-68

Background

Herpesviruses can be neutralized in vitro but remain infectious in immune hosts. One difference between these settings is the availability of immunoglobulin Fc receptors. The question therefore arises whether a herpesvirus exposed to apparently neutralizing antibody can still infect Fc receptor⁺ cells.

Principal Findings

Immune sera blocked murine gamma-herpesvirus-68 (MHV-68) infection of fibroblasts, but failed to block and even enhanced its infection of macrophages and dendritic cells. Viral glycoprotein-specific monoclonal antibodies also enhanced infection. MHV-68 appeared to be predominantly latent in macrophages regardless of whether Fc receptors were engaged, but the infection was not abortive and new virus production soon overwhelmed infected cultures. Lytically infected macrophages down-regulated MHC class I-restricted antigen presentation, endocytosis and their response to LPS.

Conclusions

IgG Fc receptors limit the neutralization of gamma-herpesviruses such as MHV-68.

Murine γ-Herpesvirus 68 Limits Naturally Occurring CD4+CD25+T Regulatory Cell Activity following Infection

During microbial infections, naturally occurring CD4+CD25+ T regulatory cells can suppress protective host responses or they can limit pathogen-induced inflammatory responses. The particular role played by these cells seems to depend upon the infectious agent being investigated. Gamma-herpesviruses are efficacious pathogens which are well-known for their ability to induce lymphoproliferative disease and to establish latency in the host. However, no studies have investigated the importance of naturally occurring CD4+CD25+ T regulatory cells during infection with these viruses. Using the murine model of gamma-herpesvirus infection, murine gamma-herpesvirus 68 (gammaHV-68), we were surprised to find that levels of the CD4+CD25+ T regulatory cell transcript, FoxP3, continued to decrease as viral latency increased and as the leukocytosis phase of the disease progressed. Consistent with these results, the decrease in FoxP3 protein expression followed similar kinetics. Along with the reduced expression of this regulatory T cell marker, we also observed diminished CD4+CD25+ T regulatory cell activity in these cells isolated from gammaHV-68-infected animals. Dendritic cells infected in vitro with gammaHV-68 did not alter the ability of normal CD4+CD25+ regulatory T cells to limit the proliferation of CD4+ Th cells following stimulation. Taken together, these studies demonstrate a decreased presence and activity of CD4+CD25+ T regulatory cells during the mononucleosis-like phase of this viral infection. These alterations in naturally occurring T regulatory cell function may help to explain the dysregulation of the host's immune response which allows the uncontrolled expansion of leukocytes as viral latency is established.

Limited IL-6 production following infection with murine gammaherpesvirus 68

Murine gammaherpesvirus 68 (gammaHV-68) was found to induce IL-6 secretion following in vitro infection of macrophages, but not cultured dendritic or epithelial cells. A detectable, but very limited IL-6 response was observed in the lungs and mediastinal lymph nodes following intranasal infection. Surprisingly, no detectable in vivo IL-6 production was observed in the spleen or sera of infected mice despite observable systemic leukocytosis. These studies demonstrate that endogenous IL-6 production contributes little to the host response, or to the viral-induced mononucleosis-like disease, due to the fact that limiting amounts of this cytokine are produced in vivo during gammaHV-68 infection.