Acute respiratory infection with mouse adenovirus type 1

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis

BACKGROUND

Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology.

METHODS

We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy.

RESULTS

Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data.

CONCLUSIONS

Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

Structure-guided AAV capsid evolution strategies for enhanced CNS gene delivery

Over the past 5 years, our laboratory has systematically developed a structure-guided library approach to evolve new adeno-associated virus (AAV) capsids with altered tissue tropism, higher transduction efficiency and the ability to evade pre-existing humoral immunity. Here, we provide a detailed protocol describing two distinct evolution strategies using structurally divergent AAV serotypes as templates, exemplified by improving CNS gene transfer efficiency in vivo. We outline four major components of our strategy: (i) structure-guided design of AAV capsid libraries, (ii) AAV library production, (iii) library cycling in single versus multiple animal models, followed by (iv) evaluation of lead AAV vector candidates in vivo. The protocol spans ~95 d, excluding gene expression analysis in vivo, and can vary depending on user experience, resources and experimental design. A distinguishing attribute of the current protocol is the focus on providing biomedical researchers with 3D structural information to guide evolution of precise 'hotspots' on AAV capsids. Furthermore, the protocol outlines two distinct methods for AAV library evolution consisting of adenovirus-enabled infectious cycling in a single species and noninfectious cycling in a cross-species manner. Notably, our workflow can be seamlessly merged with other RNA transcript-based library strategies and tailored for tissue-specific capsid selection. Overall, the procedures outlined herein can be adapted to expand the AAV vector toolkit for genetic manipulation of animal models and development of human gene therapies.

Mouse Adenovirus Type 1 Persistence Exacerbates Inflammation Induced by Allogeneic Bone Marrow Transplantation

Bone marrow transplantation (BMT) recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus. Human adenovirus persistence in mucosal lymphocytes has been described, but specific cellular reservoirs of persistence and effects of persistence on host responses to unrelated stimuli are not completely understood. We used mouse adenovirus type 1 (MAV-1) to characterize persistence of an adenovirus in its natural host and test the hypothesis that persistence increases complications of bone marrow transplantation (BMT). Following intranasal infection of C57BL/6J mice, MAV-1 DNA was detected in lung, mediastinal lymph nodes, and liver during acute infection at 7 days post infection (dpi), and at lower levels at 28 dpi that remained stable through 150 dpi. Expression of early and late viral transcripts was detected in those organs at 7 dpi but not at later time points. MAV-1 persistence was not affected by deficiency of IFN-γ. We detected no evidence of MAV-1 reactivation in vivo following allogeneic BMT of persistently infected mice. Persistent infection did not substantially affect mortality, weight loss, or pulmonary inflammation following BMT. However, T cell infiltration and increased expression of pro-inflammatory cytokines consistent with graft-versus-host disease (GVHD) were more pronounced in livers of persistently infected BMT mice than in uninfected BMT mice. These results suggest that MAV-1 persists in multiple sites without detectable evidence of ongoing replication. Our results indicate that MAV-1 persistence alters host responses to an unrelated challenge, even in the absence of detectable reactivation. Importance Long-term persistence in an infected host is an essential step in the life cycle of DNA viruses. Adenoviruses persist in their host following acute infection, but the nature of adenovirus persistence remains incompletely understood. Following intranasal infection of mice, we found that MAV-1 persists for a prolonged period in multiple organs, although we did not detect evidence of ongoing replication. Because BMT recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus in the recipient, we extended our findings using MAV-1 infection in a mouse model of BMT. MAV-1 persistence exacerbated GVHD-like inflammation following allogeneic BMT, even in the absence of virus reactivation. This novel finding suggests that adenovirus persistence has consequences, and it highlights the potential for a persistent adenovirus to influence host responses to unrelated challenges.

The RGD-binding integrins αvβ6 and αvβ8 are receptors for mouse adenovirus-1 and -3 infection

Mammalian adenoviruses (AdVs) comprise more than ~350 types including over 100 human (HAdVs) and just three mouse AdVs (MAdVs). While most HAdVs initiate infection by high affinity/avidity binding of their fiber knob (FK) protein to either coxsackievirus AdV receptor (CAR), CD46 or desmoglein (DSG)-2, MAdV-1 (M1) infection requires arginine-glycine-aspartate (RGD) binding integrins. To identify the receptors mediating MAdV infection we generated five novel reporter viruses for MAdV-1/-2/-3 (M1, M2, M3) transducing permissive murine (m) CMT-93 cells, but not B16 mouse melanoma cells expressing mCAR, human (h) CD46 or hDSG-2. Recombinant M1 or M3 FKs cross-blocked M1 and M3 but not M2 infections. Profiling of murine and human cells expressing RGD-binding integrins suggested that αvβ6 and αvβ8 heterodimers are associated with M1 and M3 infections. Ectopic expression of mβ6 in B16 cells strongly enhanced M1 and M3 binding, infection, and progeny production comparable with mαvβ6-positive CMT-93 cells, whereas mβ8 expressing cells were more permissive to M1 than M3. Anti-integrin antibodies potently blocked M1 and M3 binding and infection of CMT-93 cells and hαvβ8-positive M000216 cells. Soluble integrin αvβ6, and synthetic peptides containing the RGDLXXL sequence derived from FK-M1, FK-M3 and foot and mouth disease virus coat protein strongly interfered with M1/M3 infections, in agreement with high affinity interactions of FK-M1/FK-M3 with αvβ6/αvβ8, determined by surface plasmon resonance measurements. Molecular docking simulations of ternary complexes revealed a bent conformation of RGDLXXL-containing FK-M3 peptides on the subunit interface of αvβ6/β8, where the distal leucine residue dips into a hydrophobic pocket of β6/8, the arginine residue ionically engages αv aspartate215, and the aspartate residue coordinates a divalent cation in αvβ6/β8. Together, the RGDLXXL-bearing FKs are part of an essential mechanism for M1/M3 infection engaging murine and human αvβ6/8 integrins. These integrins are highly conserved in other mammals, and may favour cross-species virus transmission.

Enteric viruses evoke broad host immune responses resembling those elicited by the bacterial microbiome

The contributions of the viral component of the microbiome-the virome-to the development of innate and adaptive immunity are largely unknown. Here, we systematically defined the host response in mice to a panel of eukaryotic enteric viruses representing six different families. Infections with most of these viruses were asymptomatic in the mice, the magnitude and duration of which was dependent on the microbiota. Flow cytometric and transcriptional profiling of mice mono-associated with these viruses unveiled general adaptations by the host, such as lymphocyte differentiation and IL-22 signatures in the intestine, as well as numerous viral-strain-specific responses that persisted. Comparison with a dataset derived from analogous bacterial mono-association in mice identified bacterial species that evoke an immune response comparable with the viruses we examined. These results expand an understanding of the immune space occupied by the enteric virome and underscore the importance of viral exposure events.

Emerging antiviral therapeutics for human adenovirus infection: Recent developments and novel strategies

Human adenoviruses (HAdV) are ubiquitous human pathogens that cause a significant burden of respiratory, ocular, and gastrointestinal illnesses. Although HAdV infections are generally self-limiting, pediatric and immunocompromised individuals are at particular risk for developing severe disease. Currently, no approved antiviral therapies specific to HAdV exist. Recent outbreaks underscore the need for effective antiviral agents to treat life-threatening infections. In this review we will focus on recent developments in search of potential therapeutic agents for controlling HAdV infections, with a focus on those targeting post-entry stages of the virus replicative cycle.

Effects of tumor necrosis factor on viral replication and pulmonary inflammation during acute mouse adenovirus type 1 respiratory infection

CD8 T cells contribute to effective clearance of mouse adenovirus type 1 (MAV-1) and to virus-induced pulmonary inflammation. We characterized effects of a CD8 T cell effector, TNF, on MAV-1 pathogenesis. TNF inhibited MAV-1 replication in vitro. TNF deficiency or immunoneutralization had no effect on lung viral loads or viral gene expression in mice infected intranasally with MAV-1. Absence of TNF delayed virus-induced weight loss and reduced histological evidence of pulmonary inflammation, although concentrations of proinflammatory cytokines and chemokines in bronchoalveolar lavage fluid (BALF) were not significantly affected. BALF concentrations of IL-10 were greater in TNF-deficient mice compared to controls. Our data indicate that TNF is not essential for control of viral replication in vivo, but virus-induced TNF contributes to some aspects of immunopathology and disease. Redundant CD8 T cell effectors and other aspects of immune function are sufficient for antiviral and pro-inflammatory responses to acute MAV-1 respiratory infection.

Murine adenoviruses: tools for studying adenovirus pathogenesis in a natural host

Small laboratory animals are powerful models for investigating in vivo viral pathogenesis of a number of viruses. For adenoviruses (AdVs), however, species-specificity poses limitations to studying human adenoviruses (HAdVs) in mice and other small laboratory animals. Thus, this review covers work on naturally occurring mouse AdVs, primarily mouse adenovirus type 1 (MAdV-1), a member of the species Murine mastadenovirus A. Molecular genetics, virus life cycle, cell and tissue tropism, interactions with the host immune response, persistence, and host genetics of susceptibility are described. A brief discussion of MAdV-2 (member of species Murine mastadenovirus B) and MAdV-3 (member of species Murine mastadenovirus C) is included. We report the use of MAdVs in the development of vectors and vaccines.

Drug development against human adenoviruses and its advancement by Syrian hamster models

The symptoms of human adenovirus infections are generally mild and self-limiting. However, these infections have been gaining importance in recent years because of a growing number of immunocompromised patients. Solid organ and hematopoietic stem cell transplant patients are subjected to severe immunosuppressive regimes and cannot efficaciously eliminate virus infections. In these patients, adenovirus infections can develop into deadly multi-organ disseminated disease. Presently, in the absence of approved therapies, physicians rely on drugs developed for other purposes to treat adenovirus infections. As there is a need for anti-adenoviral therapies, researchers have been developing new agents and repurposing existing ones to treat adenovirus infections. There are several small molecule drugs that are being tested for their efficacy against human adenoviruses; some of these have reached clinical trials, while others are still in the preclinical phase. Besides these compounds, research on immunotherapy against adenoviral infection has made significant progress, promising another modality for treatment. The availability of an animal model confirmed the activity of some drugs already in clinical use while proving that others are inactive. This led to the identification of several lead compounds that await further development. In the present article, we review the current status of anti-adenoviral therapies and their advancement by in vivo studies in the Syrian hamster model.

Age-Dependent Effects of Immunoproteasome Deficiency on Mouse Adenovirus Type 1 Pathogenesis

Acute respiratory infection with mouse adenovirus type 1 (MAV-1) induces activity of the immunoproteasome, an inducible form of the proteasome that shapes CD8 T cell responses by enhancing peptide presentation by major histocompatibility complex (MHC) class I. We used mice deficient in all three immunoproteasome subunits (triple-knockout [TKO] mice) to determine whether immunoproteasome activity is essential for control of MAV-1 replication or inflammatory responses to acute infection. Complete immunoproteasome deficiency in adult TKO mice had no effect on MAV-1 replication, virus-induced lung inflammation, or adaptive immunity compared to C57BL/6 (B6) controls. In contrast, immunoproteasome deficiency in neonatal TKO mice was associated with decreased survival and decreased lung gamma interferon (IFN-γ) expression compared to B6 controls, although without substantial effects on viral replication, histological evidence of inflammation, or expression of the proinflammatory cytokines tumor necrosis factor alpha and interleukin-1β in lungs or other organs. T cell recruitment and IFN-γ production was similar in lungs of infected B6 and TKO mice. In lungs of uninfected B6 mice, we detected low levels of immunoproteasome subunit mRNA and protein that increased with age. Immunoproteasome subunit expression was lower in lungs of adult IFN-γ-deficient mice compared to B6 controls. Together, these results demonstrate developmental regulation of the immunoproteasome that is associated with age-dependent differences in MAV-1 pathogenesis.IMPORTANCE MAV-1 infection is a useful model to study the pathogenesis of an adenovirus in its natural host. Host factors that control MAV-1 replication and contribute to inflammation and disease are not fully understood. The immunoproteasome is an inducible component of the ubiquitin proteasome system that shapes the repertoire of peptides presented by MHC class I to CD8 T cells, influences other aspects of T cell survival and activation, and promotes production of proinflammatory cytokines. We found that immunoproteasome activity is dispensable in adult mice. However, immunoproteasome deficiency in neonatal mice increased mortality and impaired IFN-γ responses in the lungs. Baseline immunoproteasome subunit expression in lungs of uninfected mice increased with age. Our findings suggest the existence of developmental regulation of the immunoproteasome, like other aspects of host immune function, and indicate that immunoproteasome activity is a critical protective factor early in life.

Oral Vaccination with Replication-Competent Adenovirus in Mice Reveals Dissemination of the Viral Vaccine beyond the Gastrointestinal Tract

Since the 1970s, replication-competent human adenoviruses 4 and 7 have been used as oral vaccines to protect U.S. soldiers against the severe respiratory diseases caused by these viruses. These vaccines are thought to establish a digestive tract infection conferring protection against respiratory challenge through antibodies. The success of these vaccines makes replication-competent adenoviruses attractive candidates for use as oral vaccine vectors. However, the inability of human adenoviruses to replicate efficiently in laboratory animals has hampered the study of such vectors. Here, we used mouse adenovirus type 1 (MAV-1) in mice to study oral replication-competent adenovirus-based vaccines. We show that MAV-1 oral administration provides protection that recapitulates the protection against homologous respiratory challenge observed with adenovirus 4 and 7 vaccines. Moreover, live oral MAV-1 vaccine better protected against a respiratory challenge than inactivated vaccines. This protection was linked not only with the presence of MAV-1-specific antibodies but also with a better recruitment of effector CD8 T cells. However, unexpectedly, we found that such oral replication-competent vaccine systemically spread all over the body. Our results therefore support the use of MAV-1 to study replication-competent oral adenovirus-based vaccines but also highlight the fact that those vaccines can disseminate widely in the body.IMPORTANCE Replication-competent adenoviruses appear to be promising vectors for the development of oral vaccines in humans. However, the study and development of these vaccines suffer from the lack of any reliable animal model. In this study, mouse adenovirus type 1 was used to develop a small-animal model for oral replication-competent adenovirus vaccines. While this model reproduced in mice what is observed with human adenovirus oral vaccines, it also highlighted that oral immunization with such a replication-competent vaccine is associated with the systemic spread of the virus. This study is therefore of major importance for the future development of such vaccine platforms and their use in large human populations.

Fas activity mediates airway inflammation during mouse adenovirus type 1 respiratory infection

CD8 T cells play a key role in clearance of mouse adenovirus type 1 (MAV-1) from the lung and contribute to virus-induced airway inflammation. We tested the hypothesis that interactions between Fas ligand (FasL) and Fas mediate the antiviral and proinflammatory effects of CD8 T cells. FasL and Fas expression were increased in the lungs of C57BL/6 (B6) mice during MAV-1 respiratory infection. Viral replication and weight loss were similar in B6 and Fas-deficient (lpr) mice. Histological evidence of pulmonary inflammation was similar in B6 and lpr mice, but lung mRNA levels and airway proinflammatory cytokine concentrations were lower in MAV-1-infected lpr mice compared to infected B6 mice. Virus-induced apoptosis in lungs was not affected by Fas deficiency. Our results suggest that the proinflammatory effects of CD8 T cells during MAV-1 infection are mediated in part by Fas activation and are distinct from CD8 T cell antiviral functions.

Assessment of diversity of adenovirus DNA polymerase gene in recreational waters facilitated by ultracentrifugal concentration

Adenoviruses (AdV) are related to respiratory and gastrointestinal diseases in animals and human beings. Their wide genetic diversity in water bodies and their resistance to environmental conditions allow the use of AdV as a reliable marker for detection of fecal contamination. In this work, the diversity of AdV along Belo Stream - in the city of Caxias do Sul, Rio Grande do Sul, Brazil - was evaluated. Samples were compared in both concentrated and unconcentrated forms. The identification of different AdV species was performed by amplifying a partial sequence of the DNA polymerase gene. AdV was detected in 24 out of 55 concentrated samples (43.6%) and the following species were identified: human adenovirus (HAdV) species C (4/55; 7.2%), D (6/55; 10.9%), E (2/55; 3.6%), and F (9/55; 16.3%). AdV related to other mammalian hosts, such as bovine adenovirus (1/55, 1.8%) and murine adenovirus (2/55, 3.6%), have also been identified; 23.6% (13/55) of the unconcentrated samples were positive, and identified as HAdV species C (6/55, 10.9%), D (1/55, 1.8%), and F (6/55, 10.9%). Results obtained evidenced the presence and the great diversity of AdV, mainly of human origin, circulating in Belo Stream. As expected, the concentration step performed helped to detect AdV in more samples.

Mouse adenovirus type 1 infection of adipose tissue

Human adenovirus (HAdV) type 36 seropositivity has been linked to obesity in humans. That link is supported by a small number of studies using HAdV-36 infection of animals that are not natural hosts for HAdVs. In this study, we infected mice with mouse adenovirus type 1 (MAV-1), a mouse pathogen, to determine whether MAV-1 infected adipose tissue and was associated with adipose tissue inflammation and obesity. We detected MAV-1 in adipose tissue during acute MAV-1 infection, but we did not detect virus-induced increases in adipose tissue cytokine expression or histological evidence of adipose tissue inflammation during acute infection. MAV-1 did not persist in adipose tissue at later times, and we did not detect long-term adipose inflammation, increased adipose tissue mass, or body weight in infected mice. Our data indicate that MAV-1 is not associated with obesity in infected mice.

Small-size recombinant adenoviral hexon protein fragments for the production of virus-type specific antibodies

Background

Adenoviruses are common pathogens infecting animals and humans. They are classified based on serology, or genome sequence information. These methods have limitations due to lengthy procedures or lack of infectivity data. Adenoviruses are easy to produce and amenable to genetic and biochemical modifications, which makes them a powerful tool for biological studies, and clinical gene-delivery and vaccine applications. Antibodies directed against adenoviral proteins are important diagnostic tools for virus identification in vivo and in vitro, and are used to elucidate infection mechanisms, often in combination with genomic sequencing and type specific information from hyper-variable regions of structural proteins.

Results

Here we describe a novel and readily useable method for cloning, expressing and purifying small fragments of hyper-variable regions 1-6 of the adenoviral hexon protein. We used these polypeptides as antigens for generating polyclonal rabbit antibodies against human adenovirus 3 (HAdV-B3), mouse adenovirus 1 (MAdV-1) and MAdV-2 hexon. In Western immunoblots with lysates from cells infected from thirteen human and three mouse viruses, these antibodies bound to homologous full-length hexon protein and revealed variable levels of cross-reactivity to heterologous hexons. Results from immuno-fluorescence and electron microscopy studies indicated that HAdV-B3 and MAdV-2 hexon antibodies recognized native forms of hexon.

Conclusions

The procedure described here can in principle be applied to any adenovirus for which genome sequence information is available. It provides a basis for generating novel type-specific tools in diagnostics and research, and extends beyond the commonly used anti-viral antibodies raised against purified viruses or subviral components.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0822-5) contains supplementary material, which is available to authorized users.

Contributions of CD8 T cells to the pathogenesis of mouse adenovirus type 1 respiratory infection

CD8 T cells are key components of the immune response to viruses, but their roles in the pathogenesis of adenovirus respiratory infection have not been characterized. We used mouse adenovirus type 1 (MAV-1) to define CD8 T cell contributions to the pathogenesis of adenovirus respiratory infection. CD8 T cell deficiency in β2m^-/- mice had no effect on peak viral replication in lungs, but clearance of virus was delayed in β2m^-/- mice. Virus-induced weight loss and increases in bronchoalveolar lavage fluid total protein, IFN-γ, TNF-α, IL-10, CCL2, and CCL5 concentrations were less in β2m^-/- mice than in controls. CD8 T cell depletion had similar effects on virus clearance, weight loss, and inflammation. Deficiency of IFN-γ or perforin had no effect on viral replication or inflammation, but perforin-deficient mice were partially protected from weight loss. CD8 T cells promote MAV-1-induced pulmonary inflammation via a mechanism that is independent of direct antiviral effects.

Interferon-dependent immunoproteasome activity during mouse adenovirus type 1 infection

The immunoproteasome is an inducible host mechanism that aids in the clearance of damaged proteins. The immunoproteasome also influences immune function by enhancing peptide presentation by MHC class I and promotes inflammation via IκB degradation and activation of NF-κB. We used mouse adenovirus type 1 (MAV-1) to characterize the role of the immunoproteasome in adenovirus pathogenesis. Following intranasal infection of mice, immunoproteasome activity in the heart and lung was significantly increased in an IFN-γ-dependent manner. Absence of the β5i immunoproteasome subunit and pharmacological inhibition of β5i activity had minimal effects on viral replication, virus-induced cellular inflammation, or induction of cytokine expression. Likewise, the establishment of protective immunity following primary infection was not significantly altered by β5i deficiency. Thus, although immunoproteasome activity is robustly induced during acute infection with MAV-1, our data suggest that other mechanisms are capable of compensating for immunoproteasome activity to maintain antiviral immunity and appropriate inflammatory responses.

Prostaglandin E2 production during neonatal respiratory infection with mouse adenovirus type 1

Neonatal mice are more susceptible than adults to mouse adenovirus type 1 (MAV1) respiratory infection. In adult mice, MAV-1 respiratory infection induces production of prostaglandin E2 (PGE2), a lipid mediator that exerts suppressive effects on a variety of host immune functions. We tested the hypothesis that exaggerated PGE2 production in neonatal mice contributes to increased susceptibility to MAV-1. PGE2 concentrations were lower in lungs of uninfected neonatal mice than in adults. PGE2 production was induced by both MAV-1 and a nonspecific stimulus to a greater degree in neonatal mice than in adults, but only in adults was PGE2 induced in a virus-specific manner. Lung viral loads were equivalent in PGE2-deficient neonatal mice and wild type controls, as was virus-induced expression of IFN-γ, IL-17A, and CCL5 in the lungs. PGE2 deficiency had minimal effect on production of virus-specific IgG or establishment of protective immunity in neonatal mice. Collectively, our data indicate that lung PGE2 production is exaggerated early in life, but this effect does not mediate increased susceptibility to MAV-1 infection.

Xenogenic Adenoviral Vectors

Many nonhuman adenoviruses (AdVs) of simian, bovine, porcine, canine, ovine, murine, and fowl origin are being developed as gene delivery systems for recombinant vaccines and gene therapy applications. In addition to circumventing preexisting human AdV (HAdV) immunity, nonhuman AdV vectors utilize coxsackievirus-adenovirus receptor or other receptors for vector internalization, thereby expanding the range of cell types that can be targeted. Nonhuman AdV vectors also provide excellent platforms for veterinary vaccines. A specific nonhuman AdV vector when used in its species of origin could provide an excellent animal model for evaluating the vector efficacy and pathogenesis. These vectors are useful in prime–boost approaches with other AdV vectors or with other gene delivery systems including DNA immunization and viral or bacterial vectors. When multiple vector inoculations are required, nonhuman AdV vectors could supplement HAdV or other viral vectors.

Prostaglandin E2 Production and T Cell Function in Mouse Adenovirus Type 1 Infection following Allogeneic Bone Marrow Transplantation

Adenovirus infections are important complications of bone marrow transplantation (BMT). We demonstrate delayed clearance of mouse adenovirus type 1 (MAV-1) from lungs of mice following allogeneic BMT. Virus-induced prostaglandin E₂ (PGE₂) production was greater in BMT mice than in untransplanted controls, but BMT using PGE₂-deficient donors or recipients failed to improve viral clearance, and treatment of untransplanted mice with the PGE₂ analog misoprostol did not affect virus clearance. Lymphocyte recruitment to the lungs was not significantly affected by BMT. Intracellular cytokine staining of lung lymphocytes demonstrated impaired production of INF-γ and granzyme B by cells from BMT mice, and production of IFN-γ, IL-2, IL-4, and IL-17 following ex vivo stimulation was impaired in lymphocytes obtained from lungs of BMT mice. Viral clearance was not delayed in untransplanted INF-γ-deficient mice, suggesting that delayed viral clearance in BMT mice was not a direct consequence of impaired IFN-γ production. However, lung viral loads were higher in untransplanted CD8-deficient mice than in controls, suggesting that delayed MAV-1 clearance in BMT mice is due to defective CD8 T cell function. We did not detect significant induction of IFN-β expression in lungs of BMT mice or untransplanted controls, and viral clearance was not delayed in untransplanted type I IFN-unresponsive mice. We conclude that PGE₂ overproduction in BMT mice is not directly responsible for delayed viral clearance. PGE₂-independent effects on CD8 T cell function likely contribute to the inability of BMT mice to clear MAV-1 from the lungs.

Proinflammatory effects of interferon gamma in mouse adenovirus 1 myocarditis

Adenoviruses are frequent causes of pediatric myocarditis. Little is known about the pathogenesis of adenovirus myocarditis, and the species specificity of human adenoviruses has limited the development of animal models, which is a significant barrier to strategies for prevention or treatment. We have developed a mouse model of myocarditis following mouse adenovirus 1 (MAV-1) infection to study the pathogenic mechanisms of this important cause of pediatric myocarditis. Following intranasal infection of neonatal C57BL/6 mice, we detected viral replication and induction of interferon gamma (IFN-γ) in the hearts of infected mice. MAV-1 caused myocyte necrosis and induced substantial cellular inflammation that was composed predominantly of CD3(+) T lymphocytes. Depletion of IFN-γ during acute infection reduced cardiac inflammation in MAV-1-infected mice without affecting viral replication. We observed decreased contractility during acute infection of neonatal mice, and persistent viral infection in the heart was associated with cardiac remodeling and hypertrophy in adulthood. IFN-γ is a proinflammatory mediator during adenovirus-induced myocarditis, and persistent adenovirus infection may contribute to ongoing cardiac dysfunction.

IMPORTANCE

Studying the pathogenesis of myocarditis caused by different viruses is essential in order to characterize both virus-specific and generalized factors that contribute to disease. Very little is known about the pathogenesis of adenovirus myocarditis, which is a significant impediment to the development of treatment or prevention strategies. We used MAV-1 to establish a mouse model of human adenovirus myocarditis, providing the means to study host and pathogen factors contributing to adenovirus-induced cardiac disease during acute and persistent infection. The MAV-1 model will enable fundamental studies of viral myocarditis, including IFN-γ modulation as a therapeutic strategy.

IL-17 contributes to neutrophil recruitment but not to control of viral replication during acute mouse adenovirus type 1 respiratory infection

IL-17-producing CD4(+) helper T cells (Th17 cells) promote inflammatory responses to many pathogens. We used mouse adenovirus type 1 (MAV-1) to determine contributions of IL-17 to adenovirus pathogenesis. MAV-1 infection of C57BL/6 mice upregulated lung expression of IL-17 and the Th17-associated factors IL-23 and RORγt. Only CD4(+)T cells were associated with virus-specific IL-17 production. Fewer neutrophils were recruited to airways of IL-17(-/-) mice following MAV-1 infection, but there were no other differences in pulmonary inflammation between IL-17(+/+) and IL-17(-/-) mice. Mice depleted of neutrophils using anti-Gr-1 antibody had greater lung viral loads than controls. Despite impaired neutrophil recruitment, there were no differences between IL-17(+/+) and IL-17(-/-) mice in peak lung viral loads, clearance of virus from the lungs, or establishment of protective immunity. We demonstrate robust Th17 responses during MAV-1 respiratory infection, but these responses are not essential for control of virus infection or for virus-induced pulmonary inflammation.

Innate immunity to adenovirus

Human adenoviruses are the most widely used vectors in gene medicine, with applications ranging from oncolytic therapies to vaccinations, but adenovirus vectors are not without side effects. In addition, natural adenoviruses pose severe risks for immunocompromised people, yet infections are usually mild and self-limiting in immunocompetent individuals. Here we describe how adenoviruses are recognized by the host innate defense system during entry and replication in immune and nonimmune cells. Innate defense protects the host and represents a major barrier to using adenoviruses as therapeutic interventions in humans. Innate response against adenoviruses involves intrinsic factors present at constant levels, and innate factors mounted by the host cell upon viral challenge. These factors exert antiviral effects by directly binding to viruses or viral components, or shield the virus, for example, soluble factors, such as blood clotting components, the complement system, preexisting immunoglobulins, or defensins. In addition, Toll-like receptors and lectins in the plasma membrane and endosomes are intrinsic factors against adenoviruses. Important innate factors restricting adenovirus in the cytosol are tripartite motif-containing proteins, nucleotide-binding oligomerization domain-like inflammatory receptors, and DNA sensors triggering interferon, such as DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 and cyclic guanosine monophosphate-adenosine monophosphate synthase. Adenovirus tunes the function of antiviral autophagy, and counters innate defense by virtue of its early proteins E1A, E1B, E3, and E4 and two virus-associated noncoding RNAs VA-I and VA-II. We conclude by discussing strategies to engineer adenovirus vectors with attenuated innate responses and enhanced delivery features.

Prostaglandin E2 induction during mouse adenovirus type 1 respiratory infection regulates inflammatory mediator generation but does not affect viral pathogenesis

Respiratory viruses cause substantial disease and are a significant healthcare burden. Virus-induced inflammation can be detrimental to the host, causing symptoms during acute infection and leading to damage that contributes to long-term residual lung disease. Prostaglandin E₂ (PGE₂) is a lipid mediator that is increased in response to many viral infections, and inhibition of PGE₂ production during respiratory viral infection often leads to a decreased inflammatory response. We tested the hypothesis that PGE₂ promotes inflammatory responses to mouse adenovirus type 1 (MAV-1) respiratory infection. Acute MAV-1 infection increased COX-2 expression and PGE₂ production in wild type mice. Deficiency of the E prostanoid 2 receptor had no apparent effect on MAV-1 pathogenesis. Virus-induced induction of PGE₂, IFN-γ, CXCL1, and CCL5 was reduced in mice deficient in microsomal PGE synthase-1 (mPGES-1^-/- mice). However, there were no differences between mPGES-1^+/+ and mPGES-1^-/- mice in viral replication, recruitment of leukocytes to airways or lung inflammation. Infection of both mPGES‑1^+/+ and mPGES-1^-/- mice led to protection against reinfection. Thus, while PGE₂ promotes the expression of a variety of cytokines in response to acute MAV-1 infection, PGE₂ synthesis does not appear to be essential for generating pulmonary immunity.

Eicosanoids and respiratory viral infection: coordinators of inflammation and potential therapeutic targets

Viruses are frequent causes of respiratory infection, and viral respiratory infections are significant causes of hospitalization, morbidity, and sometimes mortality in a variety of patient populations. Lung inflammation induced by infection with common respiratory pathogens such as influenza and respiratory syncytial virus is accompanied by increased lung production of prostaglandins and leukotrienes, lipid mediators with a wide range of effects on host immune function. Deficiency or pharmacologic inhibition of prostaglandin and leukotriene production often results in a dampened inflammatory response to acute infection with a respiratory virus. These mediators may, therefore, serve as appealing therapeutic targets for disease caused by respiratory viral infection.

Susceptibility to acute mouse adenovirus type 1 respiratory infection and establishment of protective immunity in neonatal mice

There is an incomplete understanding of the differences between neonatal immune responses that contribute to the increased susceptibility of neonates to some viral infections. We tested the hypothesis that neonates are more susceptible than adults to mouse adenovirus type 1 (MAV-1) respiratory infection and are impaired in the ability to generate a protective immune response against a second infection. Following intranasal infection, lung viral loads were greater in neonates than in adults during the acute phase but the virus was cleared from the lungs of neonates as efficiently as it was from adult lungs. Lung gamma interferon (IFN-γ) responses were blunted and delayed in neonates, and lung viral loads were higher in adult IFN-γ(-/-) mice than in IFN-γ(+/+) controls. However, administration of recombinant IFN-γ to neonates had no effect on lung viral loads. Recruitment of inflammatory cells to the airways was impaired in neonates. CD4 and CD8 T cell responses were similar in the lungs of neonates and adults, although a transient increase in regulatory T cells occurred only in the lungs of infected neonates. Infection of neonates led to protection against reinfection later in life that was associated with increased effector memory CD8 T cells in the lungs. We conclude that neonates are more susceptible than adults to acute MAV-1 respiratory infection but are capable of generating protective immune responses.

Chest computed tomographic imaging characteristics of viral acute lower respiratory tract illnesses: a case-control study

OBJECTIVE

This study aimed to determine whether computed tomographic (CT) findings can distinguish viral lower respiratory tract illness (LRTI) from other conditions.

METHODS

Three radiologists reviewed CT images of patients with LRTI who underwent testing for respiratory viral infection. Imaging findings in subjects with positive viral assays were compared with subjects with negative assays.

RESULTS

Of 334 subjects, 93 were positive for viral LRTI. Tree-in-bud opacities and bronchial wall thickening were observed more often in subjects with viral LRTI (P < 0.05). Multifocal airspace disease occurred with similar frequency in both groups. Diffuse airspace opacification was negatively associated with viral LRTI. Pleural effusion was observed more often among subjects without viral LRTI (P < 0.001).

CONCLUSIONS

Airway inflammatory changes such as tree-in-bud opacities, bronchial wall thickening, and peribronchiolar consolidation are associated with community-acquired viral LRTI. Recognition of these findings should prompt testing for viral infection. Multifocal consolidation is commonly found in cases of viral LRTI but is nonspecific.

Limited effects of Muc1 deficiency on mouse adenovirus type 1 respiratory infection

Muc1 (MUC1 in humans) is a membrane-tethered mucin that exerts anti-inflammatory effects in the lung during bacterial infection. Muc1 and other mucins are also likely to form a protective barrier in the lung. We used mouse adenovirus type 1 (MAV-1, also known as MAdV-1) to determine the role of Muc1 in the pathogenesis of an adenovirus in its natural host. Following intranasal inoculation of wild type mice, we detected increased TNF-α, a cytokine linked to Muc1 production, but no consistent changes in the production of lung Muc1, Muc5ac or overall lung mucus production. Viral loads were modestly higher in the lungs of Muc1(-/-) mice compared to Muc1(+/+) mice at several early time points but decreased to similar levels by 14 days post infection in both groups. However, cellular inflammation and the expression of CXCL1, CCL5, and CCL2 did not significantly differ between Muc1(-/-) and Muc1(+/+) mice. Our data therefore suggest that Muc1 may contribute to a physical barrier that protects against MAV-1 respiratory infection. However, our data do not reveal an anti-inflammatory effect of Muc1 that contributes to MAV-1 pathogenesis.

The major locus for mouse adenovirus susceptibility maps to genes of the hematopoietic cell surface-expressed LY6 family

Susceptibility to mouse adenovirus type 1 is associated with the major quantitative trait locus Msq1. Msq1 was originally mapped to a 13-Mb region of mouse chromosome (Chr) 15 in crosses between SJL/J and BALB/cJ inbred mice. We have now narrowed Msq1 to a 0.75-Mb interval from 74.68 to 75.43 Mb, defined by two anonymous markers, rs8259436 and D15Spn14, using data from 1396 backcross mice. The critical interval includes 14 Ly6 or Ly6-related genes, including Ly6a (encoding Sca-1/TAP), Ly6e (Sca-2/Tsa1), Ly6g (Gr-1), and gpihbp1 (GPI-anchored high-density lipoprotein-binding protein 1), as well as the gene encoding an aldosterone synthase (Cyp11b2). The Ly6 family members are attractive candidates for virus susceptibility genes because their products are GPI-anchored membrane proteins expressed on lymphoid and myeloid cells, with proposed functions in cell adhesion and cell signaling. To determine interstrain variation in susceptibility and produce additional resources for cloning Msq1, we assayed the susceptibility phenotype of four previously untested inbred mouse strains. Susceptibility of strain 129S6/SvEvTac was subsequently localized to the Ly6 complex region, using polymorphic genetic markers on Chr 15 in a population of 271 (129S6/SvEvTac x BALB/cJ)F(1) x BALB/cJ backcross mice. We identified a major 129S6/SvEvTac susceptibility allele, Msq1(129S6), on Chr 15 in the same region as Msq1(SJL). The results indicate that a major host factor in mouse adenovirus type 1 susceptibility is likely to be a member of the Ly6 gene family.

Mouse adenovirus type 1-induced breakdown of the blood-brain barrier

Infection with mouse adenovirus type 1 (MAV-1) results in fatal acute encephalomyelitis in susceptible mouse strains via infection of brain endothelial cells. Wild-type (wt) MAV-1 causes less brain inflammation than an early region 3 (E3) null virus in C57BL/6 mice. A mouse brain microvascular endothelial cell line infected with wt MAV-1 had higher expression of mRNAs for the proinflammatory chemokines CCL2 and CCL5 than mock- and E3 null virus-infected cells. Primary mouse brain endothelial cells infected with wt virus had elevated levels of CCL2 compared to mock- or E3 null virus-infected cells. Infection of C57BL/6 mice with wt MAV-1 or the E3 null virus caused a dose-dependent breakdown of the blood-brain barrier, primarily due to direct effects of virus infection rather than inflammation. The tight junction proteins claudin-5 and occludin showed reduced surface expression on primary mouse brain endothelial cells following infection with either wt MAV-1 or the E3 null virus. mRNAs and protein for claudin-5, occludin, and zona occludens 2 were also reduced in infected cells. MAV-1 infection caused a loss of transendothelial electrical resistance in primary mouse brain endothelial cells that was not dependent on E3 or on MAV-1-induced CCL2 expression. Taken together, these results demonstrate that MAV-1 infection caused breakdown of the blood-brain barrier accompanied by decreased surface expression of tight junction proteins. Furthermore, while the MAV-1-induced pathogenesis and inflammation were dependent on E3, MAV-1-induced breakdown of the blood-brain barrier and alteration of endothelial cell function were not dependent on E3 or CCL2.

Effects of allergic airway disease on mouse adenovirus type 1 respiratory infection

Virus infection may contribute to asthma pathogenesis. In turn, a Th2-polarized pulmonary environment may increase host susceptibility to infection. We used a cockroach antigen (CRA) model of allergic airway disease to test the hypothesis that Th2 cytokine overproduction increases susceptibility to mouse adenovirus type 1 (MAV-1). CRA sensitization led to upregulated lung expression of IL-4 and IL-13, lung cellular inflammation, and exaggerated airway mucus production. Following intranasal MAV-1 infection, lung cellular inflammation was more pronounced in CRA-sensitized mice than in unsensitized mice at 7 days post-infection but not at a later time point. CRA sensitization did not significantly suppress lung IFN-gamma expression, and lung IFN-gamma expression was upregulated in both CRA-sensitized mice and unsensitized mice over the course of MAV-1 infection. Despite CRA-induced differences in pulmonary inflammation, MAV-1 viral loads in lung and spleen and MAV-1 gene expression in the lung did not differ between CRA-sensitized and unsensitized mice. Our data therefore suggest that MAV-1 pathogenesis is not affected directly or indirectly by the Th2 polarization associated with allergic airway disease.

Clinical features, adenovirus types, and local production of inflammatory mediators in adenovirus infections

BACKGROUND

Adenovirus infection manifests in many ways, with respiratory and gastrointestinal symptoms predominating.

METHODS

We performed a retrospective chart review on children evaluated at our center who had a nasal wash culture positive for adenovirus. Archived nasal washes were retrieved. Polymerase chain reaction for 15 respiratory viruses was performed on these samples. Patients who were coinfected with another virus were excluded. Adenovirus typing was performed using polymerase chain reaction primers directed at the conserved hexon gene. Bead proteomics was used to measure concentrations of inflammatory mediators.

RESULTS

Seventy-eight patients were infected only with adenovirus. The clinical diagnosis was upper respiratory infection in 60%, pneumonia in 18%, febrile seizure in 8%, and bronchiolitis in 6%. Subgroup-C and B1 infections were most common. Seventy percent of patients with upper respiratory infection and all 5 patients with bronchiolitis had a subgroup-C infection; pneumonia was caused by subgroup-B1 and C viruses. Compared with asymptomatic control patients, adenovirus infected patients had higher nasal wash concentrations of interleukin (IL)-1alpha, IL-6, inducible protein-10, macrophage inflammatory protein-1alpha, tumor necrosis factor alpha, monokine induced by gamma interferon, and interferon-alpha (P < 0.05). In addition, we found that IL-8 and IL-1alpha (P < 0.05) were higher in the nasal washes obtained from hospitalized patients than in nonhospitalized patients.

CONCLUSIONS

Adenovirus infection causes an array of clinical disease and is associated with local production of several proinflammatory cytokines. The observation that nasal wash IL-8 and IL-1alpha concentrations were higher in patients requiring hospitalization suggests that these mediators contribute to disease severity.

Adenoviruses: update on structure and function

Adenoviruses have been studied intensively for over 50 years as models of virus-cell interactions and latterly as gene vectors. With the advent of more sophisticated structural analysis techniques the disposition of most of the 13 structural proteins have been defined to a reasonable level. This review seeks to describe the functional properties of these proteins and shows that they all have a part to play in deciding the outcome of an infection and act at every level of the virus's path through the host cell. They are primarily involved in the induction of the different arms of the immune system and a better understanding of their overall properties should lead to more effective ways of combating virus infections.

Novel immunocompetent murine tumor model for evaluation of conditionally replication-competent (oncolytic) murine adenoviral vectors

Oncolytic adenoviral vectors that express immunostimulatory transgenes are currently being evaluated in clinic. Preclinical testing of these vectors has thus far been limited to immunodeficient xenograft tumor models since human adenoviruses do not replicate effectively in murine tumor cells. The effect of the immunostimulatory transgene on overall virus potency can therefore not be readily assessed in these models. Here, a model is described that allows the effective testing of mouse armed oncolytic adenovirus (MAV) vectors in immunocompetent syngeneic tumor models. These studies demonstrate that the MAV vectors have a high level of cytotoxicity in a wide range of murine tumor cells. The murine oncolytic viruses were successfully armed with murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) by a novel method which resulted in vectors with a high level of tumor-specific transgene expression. The mGM-CSF-armed MAV vectors showed an improved level of antitumor potency and induced a systemic antitumor immune response that was greater than that induced by unarmed parental vectors in immunocompetent syngeneic tumor models. Thus, the oncolytic MAV-1 system described here provides a murine homolog model for the testing of murine armed oncolytic adenovirus vectors in immunocompetent animals. The model allows evaluation of the impact of virus replication and the host immune response on overall virus potency and enables the generation of translational data that will be important for guiding the clinical development of these viruses.

Usage of integrin and heparan sulfate as receptors for mouse adenovirus type 1

Adenovirus fiber knobs are the capsid components that interact with binding receptors on cells, while an Arg-Gly-Asp (RGD) sequence usually found in the penton base protein is important for the interaction of most adenoviruses with integrin entry receptors. Mouse adenovirus type 1 (MAV-1) lacks an RGD sequence in the virion penton base protein. We tested whether an RGD sequence found in the MAV-1 fiber knob plays a role in infection. Treatment of cells with a competitor RGD peptide or a purified recombinant RGD-containing fiber knob prior to infection resulted in reduced virus yields compared to those of controls, indicating the importance of the RGD sequence for infection. An investigation of the role of integrins as possible receptors showed that MAV-1 yields were reduced in the presence of EDTA, an inhibitor of integrin binding, and in the presence of anti-alpha(v) integrin antibody. Moreover, mouse embryo fibroblasts that were genetically deficient in alpha(v) integrin yielded less virus, supporting the hypothesis that alpha(v) integrin is a likely receptor for MAV-1. We also investigated whether glycosaminoglycans play a role in MAV-1 infection. Preincubation of MAV-1 with heparin, a heparan sulfate glycosaminoglycan analog, resulted in a decrease in MAV-1 virus yields. Reduced MAV-1 infectivity was also found with cells that genetically lack heparan sulfate or cells that were treated with heparinase I. Cumulatively, our data demonstrate that the RGD sequence in the MAV-1 fiber knob plays a role in infection by MAV-1, alpha(v) integrin acts as a receptor for the virus, and cell surface heparin sulfate glycosaminoglycans are important in MAV-1 infection.

Gammaherpesvirus modulation of mouse adenovirus type 1 pathogenesis

Immune function is likely to be shaped by multiple infections over time. Infection with one pathogen can confer cross-protection against heterologous pathogens. We tested the hypothesis that latent murine gammaherpesvirus 68 (gammaHV68) infection modulates host inflammatory responses and susceptibility to mouse adenovirus type 1 (MAV-1). Mice were infected intranasally (i.n.) with gammaHV68. 21 days later, they were infected i.n. with MAV-1. We assessed cytokine and chemokine expression by quantitative reverse transcriptase real-time PCR, cellular inflammation by histology, and viral loads by quantitative real-time PCR. Previous gammaHV68 infection led to persistently upregulated IFN-gamma in lungs and spleen and persistently upregulated CCL2 and CCL5 in the lungs. Previous gammaHV68 infection amplified MAV-1-induced CCL5 upregulation and cellular inflammation in the lungs. Previous gammaHV68 infection was associated with lower MAV-1 viral loads in the spleen but not the lung. There was no significant effect of previous gammaHV68 on IFN-gamma expression or MAV-1 viral loads when the interval between infections was increased to 44 days. In summary, previous gammaHV68 infection modulated lung inflammatory responses and decreased susceptibility to a heterologous virus in an organ- and time-dependent manner.

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.

Contributions of E1A to mouse adenovirus type 1 pathogenesis following intranasal inoculation

We investigated the role of mouse adenovirus type 1 (MAV-1) early region 1A (E1A) protein in adenovirus respiratory infection. Intranasal (i.n.) inoculation of mice with wild type (wt) virus induced chemokine and cellular inflammatory responses in the lung. We observed similar responses in mice infected with an E1A-null mutant virus at the same dose, although the magnitude of these responses was lower. Levels of viral hexon gene expression were lower in the lung following infection with E1A-null virus than with wt virus. When input doses were adjusted so that equivalent viral loads were present following infection with varying doses of wt and E1A-null virus, we observed equivalent chemokine upregulation in the lung. Dissemination to the brain occurred following i.n. inoculation with equal doses of wt or E1A-null virus, but viral gene expression and viral loads were lower and the magnitude of chemokine responses was lower in brains of E1A-null virus-infected mice. CD4 and CD8 T cells and neutrophils were recruited to the brains of mice infected with either wt or E1A-null virus. Together, these data suggest that MAV-1 E1A makes important contributions to viral replication in the lung and the brain following i.n. inoculation. However, E1A is not essential for the induction of inflammatory responses in the lung or for viral dissemination out of the lung.

Enemy at the gates: forward genetics of the mouse antiviral response

The environment and the genetic constitution of both the pathogen and the host influence the severity and the outcome of viral infections. Whereas identification of the host component in humans remains challenging, recent progress in defining genes through analysis of mouse models of infection presenting natural or chemically induced variation in host susceptibility mark a fruitful period of gene discovery. This includes recognition that UNC93B1, which encodes an endocytic protein, is a susceptibility gene, providing an unexpected entry point to our understanding of the response against herpesvirus infection. By contrast, elucidation of alternative mechanisms of host resistance against mouse cytomegalovirus in inbred mouse strains has led to new insights regarding molecular recognition of the infected cells by natural killer cell MHC class I receptors. In addition, the conservation of genetic and functional aspects between mouse and human is enabling a rational pursuit of potential cures. With the continuous development of resources for experimental investigation of the genome, the production of new mutant alleles, and the phenotypic characterization of new models of infection, we predict that mouse genetic models will make an increasing contribution to our understanding of the genetic puzzle of host response to virus infection.