Receptor characterization and susceptibility of cotton rats to avian and 2009 pandemic influenza virus strains

Species-specific transcriptomic changes upon respiratory syncytial virus infection in cotton rats

The cotton rat (Sigmodon) is the gold standard pre-clinical small animal model for respiratory viral pathogens, especially for respiratory syncytial virus (RSV). However, without a reference genome or a published transcriptome, studies requiring gene expression analysis in cotton rats are severely limited. The aims of this study were to generate a comprehensive transcriptome from multiple tissues of two species of cotton rats that are commonly used as animal models (Sigmodon fulviventer and Sigmodon hispidus), and to compare and contrast gene expression changes and immune responses to RSV infection between the two species. Transcriptomes were assembled from lung, spleen, kidney, heart, and intestines for each species with a contig N50 > 1600. Annotation of contigs generated nearly 120,000 gene annotations for each species. The transcriptomes of S. fulviventer and S. hispidus were then used to assess immune response to RSV infection. We identified 238 unique genes that are significantly differentially expressed, including several genes implicated in RSV infection (e.g., Mx2, I27L2, LY6E, Viperin, Keratin 6A, ISG15, CXCL10, CXCL11, IRF9) as well as novel genes that have not previously described in RSV research (LG3BP, SYWC, ABEC1, IIGP1, CREB1). This study presents two comprehensive transcriptome references as resources for future gene expression analysis studies in the cotton rat model, as well as provides gene sequences for mechanistic characterization of molecular pathways. Overall, our results provide generalizable insights into the effect of host genetics on host-virus interactions, as well as identify new host therapeutic targets for RSV treatment and prevention.

Protection against influenza-induced Acute Lung Injury (ALI) by enhanced induction of M2a macrophages: possible role of PPARγ/RXR ligands in IL-4-induced M2a macrophage differentiation

Many respiratory viruses cause lung damage that may evolve into acute lung injury (ALI), a cytokine storm, acute respiratory distress syndrome, and ultimately, death. Peroxisome proliferator activated receptor gamma (PPARγ), a member of the nuclear hormone receptor (NHR) family of transcription factors, regulates transcription by forming heterodimers with another NHR family member, Retinoid X Receptor (RXR). Each component of the heterodimer binds specific ligands that modify transcriptional capacity of the entire heterodimer by recruiting different co-activators/co-repressors. However, the role of PPARγ/RXR ligands in the context of influenza infection is not well understood. PPARγ is associated with macrophage differentiation to an anti-inflammatory M2 state. We show that mice lacking the IL-4Rα receptor, required for M2a macrophage differentiation, are more susceptible to mouse-adapted influenza (A/PR/8/34; "PR8")-induced lethality. Mice lacking Ptgs2, that encodes COX-2, a key proinflammatory M1 macrophage mediator, are more resistant. Blocking the receptor for COX-2-induced Prostaglandin E2 (PGE2) was also protective. Treatment with pioglitazone (PGZ), a PPARγ ligand, increased survival from PR8 infection, decreased M1 macrophage gene expression, and increased PPARγ mRNA in lungs. Conversely, conditional knockout mice expressing PPARγ-deficient macrophages were significantly more sensitive to PR8-induced lethality. These findings were extended in cotton rats: PGZ blunted lung inflammation and M1 cytokine gene expression after challenge with non-adapted human influenza. To study mechanisms by which PPARγ/RXR transcription factors induce canonical M2a genes, WT mouse macrophages were treated with IL-4 in the absence or presence of rosiglitazone (RGZ; PPARγ ligand), LG100754 (LG; RXR ligand), or both. IL-4 dose-dependently induced M2a genes Arg1, Mrc1, Chil3, and Retnla. Treatment of macrophages with IL-4 and RGZ and/or LG differentially affected induction of Arg1 and Mrc1 vs. Chil3 and Retnla gene expression. In PPARγ-deficient macrophages, IL-4 alone failed to induce Arg1 and Mrc1 gene expression; however, concurrent treatment with LG or RGZ + LG enhanced IL-4-induced Arg1 and Mrc1 expression, but to a lower level than in WT macrophages, findings confirmed in the murine alveolar macrophage cell line, MH-S. These findings support a model in which PPARγ/RXR heterodimers control IL-4-induced M2a differentiation, and suggest that PPARγ/RXR agonists should be considered as important tools for clinical intervention against influenza-induced ALI.

Animal Models of Enterovirus D68 Infection and Disease

Human enterovirus D68 (EV-D68) is a globally reemerging respiratory pathogen that is associated with the development of acute flaccid myelitis (AFM) in children. Currently, there are no approved vaccines or treatments for EV-D68 infection, and there is a paucity of data related to the virus and host-specific factors that predict disease severity and progression to the neurologic syndrome. EV-D68 infection of various animal models has served as an important platform for characterization and comparison of disease pathogenesis between historic and contemporary isolates. Still, there are significant gaps in our knowledge of EV-D68 pathogenesis that constrain the development and evaluation of targeted vaccines and antiviral therapies. Continued refinement and characterization of animal models that faithfully reproduce key elements of EV-D68 infection and disease is essential for ensuring public health preparedness for future EV-D68 outbreaks.

Factors Limiting the Translatability of Rodent Model-Based Intranasal Vaccine Research to Humans

The intranasal route of vaccination presents an attractive alternative to parenteral routes and offers numerous advantages, such as the induction of both mucosal and systemic immunity, needle-free delivery, and increased patient compliance. Despite demonstrating promising results in preclinical studies, however, few intranasal vaccine candidates progress beyond early clinical trials. This discrepancy likely stems in part from the limited predictive value of rodent models, which are used frequently in intranasal vaccine research. In this review, we explored the factors that limit the translatability of rodent-based intranasal vaccine research to humans, focusing on the differences in anatomy, immunology, and disease pathology between rodents and humans. We also discussed approaches that minimize these differences and examined alternative animal models that would produce more clinically relevant research.

Neutralizing Enterovirus D68 Antibodies in Children after 2014 Outbreak, Kansas City, Missouri, USA

Antibodies to B1, B2, and D clade viruses were detected.

Enterovirus D68 (EV-D68) causes severe respiratory illness outbreaks among children, particularly those with asthma. We previously detected neutralizing antibodies against the predominant EV-D68 B1 clade in the 2014 outbreak in serum collected before the outbreak (2012–2013) from persons 24 months to 85 years of age. We recently detected neutralizing antibodies to the 2014 B1, B2, and D clade viruses in serum collected after the 2014 outbreak (April–May 2017) from 300 children 6 months to 18 years of age. B1 virus neutralizing antibodies were found in 100% of patients, even children born after 2014; B2 in 84.6%, and D in 99.6%. In 2017, titers increased with patient age and were higher than titers in 2012–2013 from comparably aged children. Rate of seronegativity was highest (15.3%) for B2 virus. Multivariate analysis revealed an association between asthma and higher titers against B2 and D viruses. EV-D68 seems to have circulated during 2014–2017.

N-Glycolylneuraminic Acid in Animal Models for Human Influenza A Virus

The first step in influenza virus infection is the binding of hemagglutinin to sialic acid-containing glycans present on the cell surface. Over 50 different sialic acid modifications are known, of which N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) are the two main species. Animal models with α2,6 linked Neu5Ac in the upper respiratory tract, similar to humans, are preferred to enable and mimic infection with unadapted human influenza A viruses. Animal models that are currently most often used to study human influenza are mice and ferrets. Additionally, guinea pigs, cotton rats, Syrian hamsters, tree shrews, domestic swine, and non-human primates (macaques and marmosets) are discussed. The presence of NeuGc and the distribution of sialic acid linkages in the most commonly used models is summarized and experimentally determined. We also evaluated the role of Neu5Gc in infection using Neu5Gc binding viruses and cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH)-/- knockout mice, which lack Neu5Gc and concluded that Neu5Gc is unlikely to be a decoy receptor. This article provides a base for choosing an appropriate animal model. Although mice are one of the most favored models, they are hardly naturally susceptible to infection with human influenza viruses, possibly because they express mainly α2,3 linked sialic acids with both Neu5Ac and Neu5Gc modifications. We suggest using ferrets, which resemble humans closely in the sialic acid content, both in the linkages and the lack of Neu5Gc, lung organization, susceptibility, and disease pathogenesis.

Microbial community structure and composition is associated with host species and sex in Sigmodon cotton rats

BACKGROUND

The cotton rat (genus Sigmodon) is an essential small animal model for the study of human infectious disease and viral therapeutic development. However, the impact of the host microbiome on infection outcomes has not been explored in this model, partly due to the lack of a comprehensive characterization of microbial communities across different cotton rat species. Understanding the dynamics of their microbiome could significantly help to better understand its role when modeling viral infections in this animal model.

RESULTS

We examined the bacterial communities of the gut and three external sites (skin, ear, and nose) of two inbred species of cotton rats commonly used in research (S. hispidus and S. fulviventer) by using 16S rRNA gene sequencing, constituting the first comprehensive characterization of the cotton rat microbiome. We showed that S. fulviventer maintained higher alpha diversity and richness than S. hispidus at external sites (skin, ear, nose), but there were no differentially abundant genera. However, S. fulviventer and S. hispidus had distinct fecal microbiomes composed of several significantly differentially abundant genera. Whole metagenomic shotgun sequencing of fecal samples identified species-level differences between S. hispidus and S. fulviventer, as well as different metabolic pathway functions as a result of differential host microbiome contributions. Furthermore, the microbiome composition of the external sites showed significant sex-based differences while fecal communities were not largely different.

CONCLUSIONS

Our study shows that host genetic background potentially exerts homeostatic pressures, resulting in distinct microbiomes for two different inbred cotton rat species. Because of the numerous studies that have uncovered strong relationships between host microbiome, viral infection outcomes, and immune responses, our findings represent a strong contribution for understanding the impact of different microbial communities on viral pathogenesis. Furthermore, we provide novel cotton rat microbiome data as a springboard to uncover the full therapeutic potential of the microbiome against viral infections.

Effect of aging on immunogenicity and efficacy of inactivated influenza vaccines in cotton rats Sigmodon hispidus

Inactivated influenza vaccines are known to be less immunogenic in human elderly in regards to serologic antibody response induced by vaccination. Accumulating evidence, however, points to a comparable effectiveness of influenza vaccines in the young and the elderly individuals. In the current study, we assessed immunogenicity and effectiveness of trivalent inactivated vaccine FluLaval in young and aged cotton rats Sigmodon hispidus and found that while serologic response to immunization was indeed reduced in older animals, comparable protection against influenza infection was afforded by prime-boost vaccination in both young and aged cotton rats. Both hemagglutination inhibition (HAI) titers and seroconversion rates were lower in the aged animals compared to the young ones. Reduction of viral load in the lung and nose, however, was comparable between young and aged animals vaccinated twice. One-time immunization with FluLaval was less efficacious at protecting the nose of aged animals, indicating that boosting of preexisting immunity can be particularly important for nasal protection in the elderly. Coincidentally, a one-time immunization with FluLaval had a detrimental effect on pulmonary pathology in the young animals, suggesting that boosting of immunity is essential for the young as well. Overall, these results suggest that reduced antibody response to and sufficient efficacy of influenza vaccines in the elderly are not two irreconcilable phenomena and that incomplete immunity to influenza can be detrimental at any age.

Characterization of humoral immune responses and degree of protection induced by influenza vaccine in cotton rats: Effects of low vaccine dose and single vs booster vaccination

Introduction

Cotton rats are a suitable model for the study of influenza disease symptoms and responses to influenza vaccination. We have previously shown that two immunizations with 15 µg whole inactivated virus (WIV) influenza vaccine could completely protect animals from infection with the H1N1pdm09 virus.

Methods

To further explore the cotton rat model, we here investigated the protective potential of a single intramuscular immunization and of prime/boost intramuscular immunizations with a low amount of antigen.

Results

A single intramuscular immunization with doses more than or equal to 0.5 µg WIV reliably evoked antibody responses and doses more than or equal to 1 µg protected the animals from virus replication in the lungs and from severe weight loss. However, clinical symptoms like an increased respiration rate were still apparent. Administration of a booster dose significantly increased the humoral immune responses but did not or only moderately improved protection from clinical symptoms.

Conclusion

Our data suggest that complete and partial protection by influenza vaccines can be mimicked in cotton rats by using specific vaccination regimens.

Herpes Simplex Virus 1 Induces Brain Inflammation and Multifocal Demyelination in the Cotton Rat Sigmodon hispidus

Our work demonstrates for the first time a direct association between infection with herpes simplex virus 1, a ubiquitous human pathogen generally associated with facial cold sores, and multifocal brain demyelination in an otherwise normal host, the cotton rat Sigmodon hispidus. For a long time, demyelinating diseases were considered to be autoimmune in nature and were studied by indirect methods, such as immunizing animals with myelin components or feeding them toxic substances that induce demyelination. Treatment against demyelinating diseases has been elusive, partially because of their unknown etiology. This work provides the first experimental evidence for the role of HSV-1 as the etiologic agent of multifocal brain demyelination in a normal host and suggests that vaccination against HSV-1 can help to combat demyelinating disorders.

Demyelinating central nervous system (CNS) disorders like multiple sclerosis (MS) and acute disseminated encephalomyelitis (ADEM) have been difficult to study and treat due to the lack of understanding of their etiology. Numerous cases point to the link between herpes simplex virus (HSV) infection and multifocal CNS demyelination in humans; however, convincing evidence from animal models has been missing. In this work, we found that HSV-1 infection of the cotton rat Sigmodon hispidus via a common route (lip abrasion) can cause multifocal CNS demyelination and inflammation. Remyelination occurred shortly after demyelination in HSV-1-infected cotton rats but could be incomplete, resulting in “scars,” further supporting an association between HSV-1 infection and multifocal demyelinating disorders. Virus was detected sequentially in the lip, trigeminal ganglia, and brain of infected animals. Brain pathology developed primarily on the ipsilateral side of the brain stem, in the cerebellum, and contralateral side of the forebrain/midbrain, suggesting that the changes may ascend along the trigeminal lemniscus pathway. Neurologic defects occasionally detected in infected animals (e.g., defective whisker touch and blink responses and compromised balance) could be representative of the brain stem/cerebellum dysfunction. Immunization of cotton rats with a split HSV-1 vaccine protected animals against viral replication and brain pathology, suggesting that vaccination against HSV-1 may protect against demyelinating disorders.

IMPORTANCE Our work demonstrates for the first time a direct association between infection with herpes simplex virus 1, a ubiquitous human pathogen generally associated with facial cold sores, and multifocal brain demyelination in an otherwise normal host, the cotton rat Sigmodon hispidus. For a long time, demyelinating diseases were considered to be autoimmune in nature and were studied by indirect methods, such as immunizing animals with myelin components or feeding them toxic substances that induce demyelination. Treatment against demyelinating diseases has been elusive, partially because of their unknown etiology. This work provides the first experimental evidence for the role of HSV-1 as the etiologic agent of multifocal brain demyelination in a normal host and suggests that vaccination against HSV-1 can help to combat demyelinating disorders.

Pathogenic difference of respiratory syncytial virus infection in cotton rats of different ages

Human respiratory syncytial virus (RSV) is the most common viral pathogen of lower respiratory tract infection worldwide. The virus selectively infects the respiratory epithelium, and causes diseases of variable severity in infants and the elderly. However, the differences in pathogenesis in the age groups remain poorly studied. Age is a major determinant of RSV disease, and the most severe morbidity and mortality occur in the infants and the elderly, because of the immature immunity in infants and declining immunity in old age. The cotton rat is a good model of RSV infection as it is naturally susceptible to RSV. In this study, we established an infant/adult/elderly RSV infection model in 3-week, 8-week and 30-week-old cotton rats and infected them with equal dose of RSV. This model exhibited airway neutrophils infiltration. In the 3-week-old group, higher viral load was observed in the lungs and noses, may due to low IFN-α/Mx2 levels. In contrast, the 8-week-old group had adequate IFN-α/Mx2 but exhibited the most obvious pulmonary inflammation and peribronchiolitis. Interestingly, the most severe pathology and delayed viral clearance in the lungs were observed in the 30-week-old group, may related to the increase of mucus induced by TNF-α and the lower antiviral effect of IFN-α. These results clearly revealed that an age-dependent severity of RSV disease and antiviral defense in the cotton rats, which may provide an effective model for personalized vaccine research and specific treatment strategies for different RSV age groups.

Novel role of gastrin releasing peptide-mediated signaling in the host response to influenza infection

Gastrin-releasing peptide (GRP) is an evolutionarily well-conserved neuropeptide that was originally recognized for its ability to mediate gastric acid secretion in the gut. More recently, however, GRP has been implicated in pulmonary lung inflammatory diseases including bronchopulmonary dysplasia, chronic obstructive pulmonary disease, emphysema, and others. Antagonizing GRP or its receptor mitigated lethality associated with the onset of viral pneumonia in a well-characterized mouse model of influenza. In mice treated therapeutically with the small-molecule GRP inhibitor, NSC77427, increased survival was accompanied by decreased numbers of GRP-producing pulmonary neuroendocrine cells, improved lung histopathology, and suppressed cytokine gene expression. In addition, in vitro studies in macrophages indicate that GRP synergizes with the prototype TLR4 agonist, lipopolysaccharide, to induce cytokine gene expression. Thus, these findings reveal that GRP is a previously unidentified mediator of influenza-induced inflammatory disease that is a potentially novel target for therapeutic intervention.

Current Understanding of Humoral Immunity to Enterovirus D68

Enterovirus D68 (EV-D68) is a pathogen that causes outbreaks of respiratory illness across the world, mostly in children, and can be especially severe in those with asthma. Clusters of acute flaccid myelitis, a poliomyelitis-like neuromuscular weakness syndrome, often occur concurrent with EV-D68 respiratory outbreaks. Seroepidemiologic studies have found that the serum of nearly everyone older than 2 to 5 years contains anti-EV-D68 neutralizing antibodies, which suggests that EV-D68 is a ubiquitous pathogen of childhood. However, knowledge of the viral epitopes against which the humoral immune response is directed is only inferred from previous studies of related viruses. Although neutralizing antibodies protect newborn mice from lethal EV-D68 inoculation via nonphysiologic routes, cotton rats have a mixed phenotype of both benefit and possible exacerbation when inoculated intranasally. The human antibody response to EV-D68 needs to be studied further to clarify the role of antibodies in protection versus pathogenesis, which might differ among respiratory and neurologic disease phenotypes.

Workshop report: Experimental animal models for universal influenza vaccines

A major challenge in influenza research is the selection of an appropriate animal model that accurately reflects the disease and the protective immune response observed in humans. A workshop organised by the EDUFLUVAC consortium, a European Union funded project coordinated by the European Vaccine Initiative, brought together experts from the influenza vaccine community with the aim to discuss the current knowledge and future perspectives for testing broadly reactive influenza vaccines in animal models. The programme included a diversity of models from well-established and publicly accepted models to cutting edge, newly developed animal models as well as ex-vivo approaches and human models. The audience concluded that different vaccine approaches may require evaluation in different animal models, depending on the type of immune response induced by the vaccine. Safety is the main concern for transition to clinical development and influenza vaccine associated enhanced disease was specifically emphasised. An efficient animal model to evaluate this aspect of safety still needs to be identified. Working with animal models requires ethical compliance and consideration of the 3R principles. Development of alternative approaches such as ex-vivo techniques is progressing but is still at an early stage and these methods are not yet suitable for broader application for vaccine evaluation. The human challenge is the ultimate model to assess influenza vaccines. However this model is expensive and not largely applicable. The currently used pre-clinical models are not yet specifically focused on studying unique aspects of a universal influenza vaccine. Further collaboration, communication and effective networking are needed for success in establishment of harmonised and standardised pre-clinical models for evaluation of new influenza vaccines. This report does not provide a complete review of the field but discusses the data presented by the speakers and discussion points raised during the meeting.

Pulmonary delivery of influenza vaccine formulations in cotton rats: site of deposition plays a minor role in the protective efficacy against clinical isolate of H1N1pdm virus

Administration of influenza vaccines to the lungs could be an attractive alternative to conventional parenteral administration. In this study, we investigated the deposition site of pulmonary delivered liquid and powder influenza vaccine formulations and its relation to their immunogenicity and protective efficacy. In vivo deposition studies in cotton rats revealed that, the powder formulation was mainly deposited in the trachea ( ∼ 65%) whereas the liquid was homogenously distributed throughout the lungs ( ∼ 96%). In addition, only 60% of the antigen in the powder formulation was deposited in the respiratory tract with respect to the liquid formulation. Immunogenicity studies showed that pulmonary delivered liquid and powder influenza formulations induced robust systemic and mucosal immune responses (significantly higher by liquids than by powders). When challenged with a clinical isolate of homologous H1N1pdm virus, all animals pulmonary administered with placebo had detectable virus in their lungs one day post challenge. In contrast, none of the vaccinated animals had detectable lung virus titers, except for two out of eight animals from the powder immunized group. Also, pulmonary vaccinated animals showed no or little signs of infection like increase in breathing frequency or weight loss upon challenge as compared to animals from the negative control group. In conclusion, immune responses induced by liquid formulation were significantly higher than responses induced by powder formulation, but the overall protective efficacy of both formulations was comparable. Thus, pulmonary immunization is capable of inducing protective immunity and the site of antigen deposition seems to be of minor relevance in inducing protection.

Serum High-Mobility-Group Box 1 as a Biomarker and a Therapeutic Target during Respiratory Virus Infections

Host-derived “danger-associated molecular patterns” (DAMPs) contribute to innate immune responses and serve as markers of disease progression and severity for inflammatory and infectious diseases. There is accumulating evidence that generation of DAMPs such as oxidized phospholipids and high-mobility-group box 1 (HMGB1) during influenza virus infection leads to acute lung injury (ALI). Treatment of influenza virus-infected mice and cotton rats with the Toll-like receptor 4 (TLR4) antagonist Eritoran blocked DAMP accumulation and ameliorated influenza virus-induced ALI. However, changes in systemic HMGB1 kinetics during the course of influenza virus infection in animal models and humans have yet to establish an association of HMGB1 release with influenza virus infection. To this end, we used the cotton rat model that is permissive to nonadapted strains of influenza A and B viruses, respiratory syncytial virus (RSV), and human rhinoviruses (HRVs). Serum HMGB1 levels were measured by an enzyme-linked immunosorbent assay (ELISA) prior to infection until day 14 or 18 post-infection. Infection with either influenza A or B virus resulted in a robust increase in serum HMGB1 levels that decreased by days 14 to 18. Inoculation with the live attenuated vaccine FluMist resulted in HMGB1 levels that were significantly lower than those with infection with live influenza viruses. RSV and HRVs showed profiles of serum HMGB1 induction that were consistent with their replication and degree of lung pathology in cotton rats. We further showed that therapeutic treatment with Eritoran of cotton rats infected with influenza B virus significantly blunted serum HMGB1 levels and improved lung pathology, without inhibiting virus replication. These findings support the use of drugs that block HMGB1 to combat influenza virus-induced ALI.

Influenza virus is a common infectious agent causing serious seasonal epidemics, and there is urgent need to develop an alternative treatment modality for influenza virus infection. Recently, host-derived DAMPs, such as oxidized phospholipids and HMGB1, were shown to be generated during influenza virus infection and cause ALI. To establish a clear link between influenza virus infection and HMGB1 as a biomarker, we have systematically analyzed temporal patterns of serum HMGB1 release in cotton rats infected with nonadapted strains of influenza A and B viruses and compared these patterns with a live attenuated influenza vaccine and infection by other respiratory viruses. Towards development of a new therapeutic modality, we show herein that blocking serum HMGB1 levels by Eritoran improves lung pathology in influenza B virus-infected cotton rats. Our study is the first report of systemic HMGB1 as a potential biomarker of severity in respiratory virus infections and confirms that drugs that block virus-induced HMGB1 ameliorate ALI.

Syrian Hamster as an Animal Model for the Study of Human Influenza Virus Infection

Ferrets and mice are frequently used as animal models for influenza research. However, ferrets are demanding in terms of housing space and handling, whereas mice are not naturally susceptible to infection with human influenza A or B viruses. Therefore, prior adaptation of human viruses is required for their use in mice. In addition, there are no mouse-adapted variants of the recent H3N2 viruses, because these viruses do not replicate well in mice. In this study, we investigated the susceptibility of Syrian hamsters to influenza viruses with a view to using the hamster model as an alternative to the mouse model. We found that hamsters are sensitive to influenza viruses, including the recent H3N2 viruses, without adaptation. Although the hamsters did not show weight loss or clinical signs of H3N2 virus infection, we observed pathogenic effects in the respiratory tracts of the infected animals. All of the H3N2 viruses tested replicated in the respiratory organs of the hamsters, and some of them were detected in the nasal washes of infected animals. Moreover, a 2009 pandemic (pdm09) virus and a seasonal H1N1 virus, as well as one of the two H3N2 viruses, but not a type B virus, were transmissible by the airborne route in these hamsters. Hamsters thus have the potential to be a small-animal model for the study of influenza virus infection, including studies of the pathogenicity of H3N2 viruses and other strains, as well as for use in H1N1 virus transmission studies.IMPORTANCE We found that Syrian hamsters are susceptible to human influenza viruses, including the recent H3N2 viruses, without adaptation. We also found that a pdm09 virus and a seasonal H1N1 virus, as well as one of the H3N2 viruses, but not a type B virus tested, are transmitted by the airborne route in these hamsters. Syrian hamsters thus have the potential to be used as a small-animal model for the study of human influenza viruses.

Immunization with Live Human Rhinovirus (HRV) 16 Induces Protection in Cotton Rats against HRV14 Infection

Human rhinoviruses (HRVs) are the main cause of cold-like illnesses, and currently no vaccine or antiviral therapies against HRVs are available to prevent or mitigate HRV infection. There are more than 150 antigenically heterogeneous HRV serotypes, with ∼90 HRVs belonging to major group species A and B. Development of small animal models that are susceptible to infection with major group HRVs would be beneficial for vaccine research. Previously, we showed that the cotton rat (Sigmodon hispidus) is semi-permissive to HRV16 (major group, species HRV-A virus) infection, replicating in the upper and lower respiratory tracts with measurable pathology, mucus production, and expression of inflammatory mediators. Herein, we report that intranasal infection of cotton rats with HRV14 (major group, species HRV-B virus) results in isolation of infectious virus from the nose and lung. Similar to HRV16, intramuscular immunization with live HRV14 induces homologous protection that correlated with high levels of serum neutralizing antibodies. Vaccination and challenge experiments with HRV14 and HRV16 to evaluate the development of cross-protective immunity demonstrate that intramuscular immunization with live HRV16 significantly protects animals against HRV14 challenge. Determination of the immunological mechanisms involved in heterologous protection and further characterization of infection with other major HRV serotypes in the cotton rat could enhance the robustness of the model to define heterotypic relationships between this diverse group of viruses and thereby increase its potential for development of a multi-serotype HRV vaccine.

Enterovirus D-68 Infection, Prophylaxis, and Vaccination in a Novel Permissive Animal Model, the Cotton Rat (Sigmodon hispidus)

In recent years, there has been a significant increase in detection of Enterovirus D-68 (EV-D68) among patients with severe respiratory infections worldwide. EV-D68 is now recognized as a re-emerging pathogen; however, due to lack of a permissive animal model for EV-D68, a comprehensive understanding of the pathogenesis and immune response against EV-D68 has been hampered. Recently, it was shown that EV-D68 has a strong affinity for α2,6-linked sialic acids (SAs) and we have shown previously that α2,6-linked SAs are abundantly present in the respiratory tract of cotton rats (Sigmodon hispidus). Thus, we hypothesized that cotton rats could be a potential model for EV-D68 infection. Here, we evaluated the ability of two recently isolated EV-D68 strains (VANBT/1 and MO/14/49), along with the historical prototype Fermon strain (ATCC), to infect cotton rats. We found that cotton rats are permissive to EV-D68 infection without virus adaptation. The different strains of EV-D68 showed variable infection profiles and the ability to produce neutralizing antibody (NA) upon intranasal infection or intramuscular immunization. Infection with the VANBT/1 resulted in significant induction of pulmonary cytokine gene expression and lung pathology. Intramuscular immunization with live VANBT/1 or MO/14/49 induced strong homologous antibody responses, but a moderate heterologous NA response. We showed that passive prophylactic administration of serum with high content of NA against VANBT/1 resulted in an efficient antiviral therapy. VANBT/1-immunized animals showed complete protection from VANBT/1 challenge, but induced strong pulmonary Th1 and Th2 cytokine responses and enhanced lung pathology, indicating the generation of exacerbated immune response by immunization. In conclusion, our data illustrate that the cotton rat is a powerful animal model that provides an experimental platform to investigate pathogenesis, immune response, anti-viral therapies and vaccines against EV-D68 infection.

Evaluation of the potential effects of AS03-adjuvanted A(H1N1)pdm09 vaccine administration on the central nervous system of non-primed and A(H1N1)pdm09-primed cotton rats

An increased risk of narcolepsy following administration of an AS03-adjuvanted A(H1N1)pdm09 pandemic influenza vaccine (Pandemrix™) was described in children and adolescents in certain European countries. We investigated the potential effects of administration of the AS03-adjuvanted vaccine, non-adjuvanted vaccine antigen and AS03 Adjuvant System alone, on the central nervous system (CNS) in one-month-old cotton rats. Naïve or A(H1N1)pdm09 virus-primed animals received 2 or 3 intramuscular injections, respectively, of test article or saline at 2-week intervals. Parameters related to systemic inflammation (hematology, serum IL-6/IFN-γ/TNF-α) were assessed. Potential effects on the CNS were investigated by histopathological evaluation of brain sections stained with hematoxylin-and-eosin, or by immunohistochemical staining of microglia, using Iba1 and CD68 as markers for microglia identification/activation, albumin as indicator of vascular leakage, and hypocretin. We also determined cerebrospinal fluid (CSF) hypocretin levels and hemagglutination-inhibiting antibody titers. Immunogenicity of the AS03-adjuvanted A(H1N1)pdm09 pandemic influenza vaccine was confirmed by the induction of hemagglutination-inhibiting antibodies. Both AS03-adjuvanted vaccine and AS03 alone activated transient innate (neutrophils/eosinophils) immune responses. No serum cytokines were detected. CNS analyses revealed neither microglia activation nor inflammatory cellular infiltrates in the brain. No differences between treatment groups were detected for albumin extravascular leakage, CSF hypocretin levels, numbers of hypocretin-positive neuronal bodies or distributions of hypocretin-positive axonal/dendritic projections. Consequently, there was no evidence that intramuscular administration of the test articles promoted inflammation or damage in the CNS, or blood-brain barrier disruption, in this model.

Novel strategies for targeting innate immune responses to influenza

We previously reported that TLR4(-/-) mice are refractory to mouse-adapted A/PR/8/34 (PR8) influenza-induced lethality and that therapeutic administration of the TLR4 antagonist Eritoran blocked PR8-induced lethality and acute lung injury (ALI) when given starting 2 days post infection. Herein we extend these findings: anti-TLR4- or -TLR2-specific IgG therapy also conferred significant protection of wild-type (WT) mice from lethal PR8 infection. If treatment is initiated 3 h before PR8 infection and continued daily for 4 days, Eritoran failed to protect WT and TLR4(-/-) mice, implying that Eritoran must block a virus-induced, non-TLR4 signal that is required for protection. Mechanistically, we determined that (i) Eritoran blocks high-mobility group B1 (HMGB1)-mediated, TLR4-dependent signaling in vitro and circulating HMGB1 in vivo, and an HMGB1 inhibitor protects against PR8; (ii) Eritoran inhibits pulmonary lung edema associated with ALI; (iii) interleukin (IL)-1β contributes significantly to PR8-induced lethality, as evidenced by partial protection by IL-1 receptor antagonist (IL-1Ra) therapy. Synergistic protection against PR8-induced lethality was achieved when Eritoran and the antiviral drug oseltamivir were administered starting 4 days post infection. Eritoran treatment does not prevent development of an adaptive immune response to subsequent PR8 challenge. Overall, our data support the potential of a host-targeted therapeutic approach to influenza infection.

Epithelial cell lines of the cotton rat (Sigmodon hispidus) are highly susceptible in vitro models to zoonotic Bunya-, Rhabdo-, and Flaviviruses

Background

Small mammals such as bats and rodents have been increasingly recognized as reservoirs of novel potentially zoonotic pathogens. However, few in vitro model systems to date allow assessment of zoonotic viruses in a relevant host context. The cotton rat (Sigmodon hispidus) is a New World rodent species that has a long-standing history as an experimental animal model due to its unique susceptibility to human viruses. Furthermore, wild cotton rats are associated with a large variety of known or potentially zoonotic pathogens.

Methods

A method for the isolation and culture of airway epithelial cell lines recently developed for bats was applied for the generation of rodent airway and renal epithelial cell lines from the cotton rat. Continuous cell lines were characterized for their epithelial properties as well as for their interferon competence. Susceptibility to members of zoonotic Bunya-, Rhabdo-, and Flaviviridae, in particular Rift Valley fever virus (RVFV), vesicular stomatitis virus (VSV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) was tested. Furthermore, novel arthropod-derived viruses belonging to the families Bunya-, Rhabdo-, and Mesoniviridae were tested.

Results

We successfully established airway and kidney epithelial cell lines from the cotton rat, and characterized their epithelial properties. Cells were shown to be interferon-competent. Viral infection assays showed high-titre viral replication of RVFV, VSV, WNV, and TBEV, as well as production of infectious virus particles. No viral replication was observed for novel arthropod-derived members of the Bunya-, Rhabdo-, and Mesoniviridae families in these cell lines.

Conclusion

In the current study, we showed that newly established cell lines from the cotton rat can serve as host-specific in vitro models for viral infection experiments. These cell lines may also serve as novel tools for virus isolation, as well as for the investigation of virus-host interactions in a relevant host species.

Preparation of quadri-subtype influenza virus-like particles using bovine immunodeficiency virus gag protein

Influenza VLPs comprised of hemagglutinin (HA), neuraminidase (NA), and matrix (M1) proteins have been previously used for immunological and virological studies. Here we demonstrated that influenza VLPs can be made in Sf9 cells by using the bovine immunodeficiency virus gag (Bgag) protein in place of M1. We showed that Bgag can be used to prepare VLPs for several influenza subtypes including H1N1 and H10N8. Furthermore, by using Bgag, we prepared quadri-subtype VLPs, which co-expressed within the VLP the four HA subtypes derived from avian-origin H5N1, H7N9, H9N2 and H10N8 viruses. VLPs showed hemagglutination and neuraminidase activities and reacted with specific antisera. The content and co-localization of each HA subtype within the quadri-subtype VLP were evaluated. Electron microscopy showed that Bgag-based VLPs resembled influenza virions with the diameter of 150-200nm. This is the first report of quadri-subtype design for influenza VLP and the use of Bgag for influenza VLP preparation.

Efficacy of the Herpes Simplex Virus 2 (HSV-2) Glycoprotein D/AS04 Vaccine against Genital HSV-2 and HSV-1 Infection and Disease in the Cotton Rat Sigmodon hispidus Model

Subunit vaccines based on the herpes simplex virus 2 (HSV-2) glycoprotein D (gD-2) have been the major focus of HSV-2 vaccine development for the past 2 decades. Based on the promising data generated in the guinea pig model, a formulation containing truncated gD-2, aluminum salt, and MPL (gD/AS04) advanced to clinical trials. The results of these trials, however, were unexpected, as the vaccine protected against HSV-1 infection but not against HSV-2. To address this discrepancy, we developed a Depot medroxyprogesterone acetate (DMPA)-treated cotton rat Sigmodon hispidus model of HSV-2 and HSV-1 genital infection. The severity of HSV-1 genital herpes was less than that of HSV-2 genital herpes in cotton rats, and yet the model allowed for comparative evaluation of gD/AS04 immunogenicity and efficacy. Cotton rats were intramuscularly vaccinated using a prime boost strategy with gD/AS04 (Simplirix vaccine) or control vaccine formulation (hepatitis B vaccine FENDrix) and subsequently challenged intravaginally with HSV-2 or HSV-1. The gD/AS04 vaccine was immunogenic in cotton rats and induced serum IgG directed against gD-2 and serum HSV-2 neutralizing antibodies but failed to efficiently protect against HSV-2 disease or to decrease the HSV-2 viral load. However, gD/AS04 significantly reduced vaginal titers of HSV-1 and better protected animals against HSV-1 compared to HSV-2 genital disease. The latter finding is generally consistent with the clinical outcome of the Herpevac trial of Simplirix. Passive transfer of serum from gD/AS04-immunized cotton rats conferred stronger protection against HSV-1 genital disease. These findings suggest the need for alternative vaccine strategies and the identification of new correlates of protection.

IMPORTANCE

In spite of the high health burden of genital herpes, there is still no effective intervention against the disease. The significant gap in knowledge on genital herpes pathogenesis has been further highlighted by the recent failure of GSK HSV-2 vaccine Simplirix (gD/AS04) to protect humans against HSV-2 and the surprising finding that the vaccine protected against HSV-1 genital herpes instead. In this study, we report that gD/AS04 has higher efficacy against HSV-1 compared to HSV-2 genital herpes in the novel DMPA-synchronized cotton rat model of HSV-1 and HSV-2 infection. The findings help explain the results of the Simplirix trial.

Animal models for influenza viruses: implications for universal vaccine development

Influenza virus infections are a significant cause of morbidity and mortality in the human population. Depending on the virulence of the influenza virus strain, as well as the immunological status of the infected individual, the severity of the respiratory disease may range from sub-clinical or mild symptoms to severe pneumonia that can sometimes lead to death. Vaccines remain the primary public health measure in reducing the influenza burden. Though the first influenza vaccine preparation was licensed more than 60 years ago, current research efforts seek to develop novel vaccination strategies with improved immunogenicity, effectiveness, and breadth of protection. Animal models of influenza have been essential in facilitating studies aimed at understanding viral factors that affect pathogenesis and contribute to disease or transmission. Among others, mice, ferrets, pigs, and nonhuman primates have been used to study influenza virus infection in vivo, as well as to do pre-clinical testing of novel vaccine approaches. Here we discuss and compare the unique advantages and limitations of each model.

PROPHYLACTIC ANTIBODY TREATMENT AND INTRAMUSCULAR IMMUNIZATION REDUCE INFECTIOUS HUMAN RHINOVIRUS 16 LOAD IN THE LOWER RESPIRATORY TRACT OF CHALLENGED COTTON RATS

Human rhinoviruses (HRV) represent the single most important etiological agents of the common cold and are the most frequent cause of acute respiratory infections in humans. Currently the performance of available animal models for immunization studies using HRV challenge is very limited. The cotton rat (Sigmodon hispidus) is a well-recognized model for the study of human respiratory viral infections. In this work we show that, without requiring any genetic modification of either the host or the virus, intranasal infection of cotton rats with HRV16 resulted in measurable lower respiratory tract pathology, mucus production, and expression of interferon-activated genes. Intramuscular immunization with live HRV16 generated robust protective immunity that correlated with high serum levels of neutralizing antibodies. In addition, cotton rats treated prophylactically with hyperimmune anti-HRV16 serum were protected against HRV16 intranasal challenge. Finally, protection by immunization was efficiently transferred from mothers to newborn animals resulting in a substantial reduction of infectious virus loads in the lung following intranasal challenge. Overall, our results demonstrate that the cotton rat provides valuable additional model development options for testing vaccines and prophylactic therapies against rhinovirus infection.

Modeling Human Respiratory Viral Infections in the Cotton Rat (Sigmodon hispidus)

For over three decades, cotton rats have been a preferred model for human Respiratory Syncytial Virus (RSV) infection and pathogenesis, and a reliable model for an impressive list of human respiratory pathogens including adenoviruses, para influenza virus, measles, and human metapneumo virus. The most significant contribution of the cotton rat to biomedical research has been the development of anti-RSV antibodies for prophylactic use in high-risk infants. More recently, however, the cotton rat model has been further explored as a model for infection with other respiratory viral pathogens including influenza and rhinovirus.Together with RSV, these viruses inflict the greatest impact on the human respiratory health.This review will focus on the characteristics of these new models and their potential contribution to the development of new therapies.

The experimental aerosol transmission of influenza virus

The threat of a virulent, highly transmissible pandemic virus has motivated an escalating research effort to identify the transmissible genotypes of animal viruses that cross over into the human population (animal–human transmission) and sustain human–human transmission. In addition to the pursuit of the viral genotype, a greater understanding of the host-virus phenotype of infectiousness, transmissibility and susceptibility will be required. This review examines experimental animal transmission of influenza for insights into human influenza transmission. Transmission is viewed as sequential steps that the virus must pass critical thresholds to achieve transmission and ultimately survival in the human host. In particular, a quantitative understanding in animal models of viral replication efficiency, airway viral load, exhaled viral aerosol load, environmental virus survival and host susceptibility will likely yield important insights. Computational modeling will enhance animal model data, as well as guide the use of pandemic mitigation strategies.

Inhibition of primary clinical isolates of human parainfluenza virus by DAS181 in cell culture and in a cotton rat model

DAS181 is a novel drug in development for the treatment of influenza as well as human parainfluenza viruses (hPIVs). Previous studies demonstrated that DAS181 inhibited laboratory strains of hPIV, but no tests were conducted with primary clinical isolates of hPIV. To fill this gap, we studied six primary isolates including hPIV-2 and hPIV-3. First tests showed that the amplification of all viruses in vitro was reproducibly inhibited with DAS181 drug concentrations ranging between 0.1 and 1nM. An hPIV-3 primary clinical isolate was then tested in a cotton rat model for sensitivity to 0.3-1mg/kg drug treatments. Results showed that virus amplification in the lower respiratory tract was significantly and reproducibly inhibited by drug. Together, experiments demonstrated that DAS181 inhibited primary clinical isolates of hPIV in vitro and in vivo at doses similar to those previously described for inhibition of laboratory hPIV and influenza virus isolates.

The TLR4 antagonist Eritoran protects mice from lethal influenza infection

There is a pressing need to develop alternatives to annual influenza vaccines and antiviral agents licensed for mitigating influenza infection. Previous studies reported that acute lung injury caused by chemical or microbial insults is secondary to the generation of host-derived, oxidized phospholipid that potently stimulates Toll-like receptor 4 (TLR4)-dependent inflammation. Subsequently, we reported that Tlr4(-/-) mice are highly refractory to influenza-induced lethality, and proposed that therapeutic antagonism of TLR4 signalling would protect against influenza-induced acute lung injury. Here we report that therapeutic administration of Eritoran (also known as E5564)-a potent, well-tolerated, synthetic TLR4 antagonist-blocks influenza-induced lethality in mice, as well as lung pathology, clinical symptoms, cytokine and oxidized phospholipid expression, and decreases viral titres. CD14 and TLR2 are also required for Eritoran-mediated protection, and CD14 directly binds Eritoran and inhibits ligand binding to MD2. Thus, Eritoran blockade of TLR signalling represents a novel therapeutic approach for inflammation associated with influenza, and possibly other infections.

Intranasal vaccination with H5, H7 and H9 hemagglutinins co-localized in a virus-like particle protects ferrets from multiple avian influenza viruses

Avian influenza H5, H7 and H9 viruses top the World Health Organization's (WHO) list of subtypes with the greatest pandemic potential. Here we describe a recombinant virus-like particle (VLP) that co-localizes hemagglutinin (HA) proteins derived from H5N1, H7N2, and H9N2 viruses as an experimental vaccine against these viruses. A baculovirus vector was configured to co-express the H5, H7, and H9 genes from A/Viet Nam/1203/2004 (H5N1), A/New York/107/2003 (H7N2) and A/Hong Kong/33982/2009 (H9N2) viruses, respectively, as well as neuraminidase (NA) and matrix (M1) genes from A/Puerto Rico/8/1934 (H1N1) virus. Co-expression of these genes in Sf9 cells resulted in production of triple-subtype VLPs containing HA molecules derived from the three influenza viruses. The triple-subtype VLPs exhibited hemagglutination and neuraminidase activities and morphologically resembled influenza virions. Intranasal vaccination of ferrets with the VLPs resulted in induction of serum antibody responses and efficient protection against experimental challenges with H5N1, H7N2, and H9N2 viruses.

The cotton rat Sigmodon hispidus model of respiratory syncytial virus infection

The cotton rat Sigmodon hispidus is a New World rodent that has become an important model of respiratory syncytial virus (RSV) infection. This small animal is relatively permissive to RSV and can be infected throughout life. It recapitulates the pathology associated with the FI-RSV vaccine-enhanced disease, the phenomenon of maternally transmitted immunity and the ability of passive immunity to suppress efficacy of RSV vaccines. Different highly susceptible human cohort scenarios have been modeled in the cotton rat, including RSV disease in infants, elderly, and immunosuppressed individuals. The cotton rat has accurately predicted efficacy and dose of antibody immunoprophylaxis, and the lack of efficacy of antibody immunotherapy for disease treatment. With the recent development of molecular reagents and tools for the model, the cotton rat is an important model of RSV infection to consider for vaccine and drug testing, and will continue to advance our understanding of RSV disease pathogenesis.