Exogenous administration of vascular endothelial growth factor prior to human respiratory syncytial virus a2 infection reduces pulmonary pathology in neonatal lambs and alters epithelial innate immune responses

A model of respiratory syncytial virus (RSV) infection of infants in newborn lambs

Many animal models have been established for respiratory syncytial virus (RSV) infection of infants with the purpose of studying the pathogenesis, immunological response, and pharmaceutical testing and the objective of finding novel therapies and preventive measures. This review centers on a neonatal lamb model of RSV infection that has similarities to RSV infection of infants. It includes a comprehensive description of anatomical and immunological similarities between ovine and human lungs along with comparison of pulmonary changes and immune responses with RSV infection. These features make the newborn lamb an effective model for investigating key aspects of RSV infection in infants. The importance of RSV lamb model application in preclinical therapeutic trials and current updates on new studies with the RSV-infected neonatal lamb are also highlighted.

Kinetics of Respiratory Syncytial Virus (RSV) Memphis Strain 37 (M37) Infection in the Respiratory Tract of Newborn Lambs as an RSV Infection Model for Human Infants

Rationale

Respiratory syncytial virus (RSV) infection in preterm and newborn infants can result in severe bronchiolitis and hospitalization. The lamb lung has several key features conducive to modeling RSV infection in human infants, including susceptibility to human strains of RSV such as the A2, Long, and Memphis Strain 37 (M37). In this study, the kinetics of M37 infection was investigated in newborn lambs in order to better define clinical, viral, physiological, and immunological parameters as well as the pathology and lesions.

Methods

Newborn lambs were nebulized with M37 hRSV (6 mL of 1.27 x 10⁷ FFU/mL), monitored daily for clinical responses, and respiratory tissues were collected from groups of lambs at days 1, 3, 4, 6, and 8 post-inoculation for the assessment of viral replication parameters, lesions and also cellular, immunologic and inflammatory responses.

Results

Lambs had increased expiratory effort (forced expiration) at days 4, 6, and 8 post-inoculation. Nasal wash lacked RSV titers at day 1, but titers were present at low levels at days 3 (peak), 4, and 8. Viral titers in bronchoalveolar lavage fluid (BALF) reached a plateau at day 3 (4.6 Log₁₀ FFU/mL), which was maintained until day 6 (4.83 Log₁₀ FFU/mL), and were markedly reduced or absent at day 8. Viral RNA levels (detected by RT-qPCR) in BALF were indistinguishable at days 3 (6.22 ± 0.08 Log₁₀ M37 RNA copies/mL; mean ± se) and 4 (6.20 ± 0.16 Log₁₀ M37 RNA copies/mL; mean ± se) and increased slightly on day 6 (7.15 ± 0.2 Log₁₀ M37 RNA copies/mL; mean ± se). Viral antigen in lung tissue as detected by immunohistochemistry was not seen at day 1, was present at days 3 and 4 before reaching a peak by day 6, and was markedly reduced by day 8. Viral antigen was mainly present in airways (bronchi, bronchioles) at day 3 and was increasingly present in alveolar cells at days 4 and 6, with reduction at day 8. Histopathologic lesions such as bronchitis/bronchiolitis, epithelial necrosis and hyperplasia, peribronchial lymphocyte infiltration, and syncytial cells, were consistent with those described previously for lambs and infants.

Conclusion

This work demonstrates that M37 hRSV replication in the lower airways of newborn lambs is robust with peak replication on day 3 and sustained until day 6. These findings, along with the similarities of lamb lung to those of infants in terms of alveolar development, airway branching and epithelium, susceptibility to human RSV strains, lesion characteristics (bronchiolitis), lung size, clinical parameters, and immunity, further establish the neonatal lamb as a model with key features that mimic RSV infection in infants.

Respiratory syncytial virus (RSV) and its propensity for causing bronchiolitis

Infants and young children with acute onset of wheezing and reduced respiratory airflows are often diagnosed with obstruction and inflammation of the small bronchiolar airways, ie bronchiolitis. The most common aetological agents causing bronchiolitis in young children are the respiratory viruses, and of the commonly encountered respiratory viruses, respiratory syncytial virus (RSV) has a propensity for causing bronchiolitis. Indeed, RSV bronchiolitis remains the major reason why previously healthy infants are admitted to hospital. Why RSV infection is such a predominant cause of bronchiolitis is the subject of this review. By reviewing the available histopathology of RSV bronchiolitis, both in humans and relevant animal models, we identify hallmark features of RSV infection of the distal airways and focus attention on the consequences of columnar cell cytopathology occurring in the bronchioles, which directly impacts the development of bronchiolar obstruction, inflammation and disease. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Delayed VEGF treatment enhances angiogenesis and recovery after neonatal focal rodent stroke

Neonatal stroke occurs in one in 4,000 live births and leads to significant morbidity and mortality. Approximately two thirds of the survivors have long-term sequelae including seizures and neurological deficits. However, the pathophysiological mechanisms of recovery after neonatal stroke are not clearly understood, and preventive measures and treatments are nonexistent in the clinical setting. In this study, we investigated the effect of vascular endothelial growth factor (VEGF) treatment on histological recovery and angiogenic response to the developing brain after an ischemic insult. Ten-day-old Sprague-Dawley rats underwent right middle cerebral arterial occlusion (MCAO) for 1.5 h. Diffusion-weighted MRI during occlusion confirmed focal ischemia that was then followed by reperfusion. On group of animals received 5-bromo-2-deoxyuridine and sacrificed at postnatal day (P)18 or P25. A second group of animals was treated with VEGF (1.5 µg/kg, icv) or phosphate-buffered saline (PBS) at P18 and perfusion fixed at P25. Based on Nissl and iron staining, a single VEGF injection reduced the injury score, compared to the animals that underwent MCAO and PBS injection. Furthermore, neurodegeneration represented by neuronal nuclei staining was markedly diminished. In addition, animals treated with VEGF revealed a positive trend in endothelial proliferation and a significant increase in total vessel volume in the peri-infarct region of the caudate. The number of Iba1-positive microglial cells was significantly reduced after a single VEGF injection, and myelin basic protein expression was enhanced in the caudate after ischemia without an effect of VEGF treatment. In conclusion, delayed treatment with VEGF ameliorates injury, promotes endothelial cell proliferation, and increases total vascular volume following neonatal stroke. These results suggest that VEGF has a neuroprotective effect, in part by enhancing endogenous angiogenesis. These data contribute to a better understanding of neonatal stroke.

Human respiratory syncytial virus memphis 37 causes acute respiratory disease in perinatal lamb lung

Respiratory syncytial virus (RSV) is the leading cause of hospitalization due to respiratory illness among infants and young children of industrialized countries. There is a lack of understanding of the severe disease mechanisms as well as limited treatment options, none of which are fully satisfactory. This is partly due to lack of a relevant animal model of perinatal RSV infection that mimics moderate to severe disease in infants. We and others have shown mild disease in perinatal lambs with either a bovine or a human A2 strain of RSV. The Memphis 37 clinical strain of human RSV has been used to produce mild to moderate upper respiratory disease in healthy adult volunteers. We hypothesized that the Memphis 37 strain of RSV would infect perinatal lambs and produce clinical disease similar to that in human infants. Perinatal (3- to 5-day-old) lambs were inoculated intranasally with 2 mL/nostril of 1×10⁵ focus-forming units (FFU)/mL (n=2) or 2.1×10⁸ FFU/mL (n=3) of RSV Memphis 37. Clinical signs, gross and histological lesions, and immune and inflammatory responses were assessed. Memphis 37 caused moderate to severe gross and histologic lesions along with increased mRNA expression of macrophage inflammatory protein. Clinically, four of the five infected lambs had a mild to severe increase in expiratory effort. Intranasally administered RSV strain Memphis 37 infects neonatal lambs with gross, histologic, and immune responses similar to those observed in human infants.

Increased concentration of iodide in airway secretions is associated with reduced respiratory syncytial virus disease severity

Recent studies have revealed that the human and nonrodent mammalian airway mucosa contains an oxidative host defense system. This three-component system consists of the hydrogen peroxide (H2O2)-producing enzymes dual oxidase (Duox)1 and Duox2, thiocyanate (SCN(-)), and secreted lactoperoxidase (LPO). The LPO-catalyzed reaction between H2O2 and SCN(-) yields the bactericidal hypothiocyanite (OSCN(-)) in airway surface liquid (ASL). Although SCN(-) is the physiological substrate of LPO, the Duox/LPO/halide system can generate hypoiodous acid when the iodide (I(-)) concentration is elevated in ASL. Because hypoiodous acid, but not OSCN(-), inactivates respiratory syncytial virus (RSV) in cell culture, we used a lamb model of RSV to test whether potassium iodide (KI) could enhance this system in vivo. Newborn lambs received KI by intragastric gavage or were left untreated before intratracheal inoculation of RSV. KI treatment led to a 10-fold increase in ASL I(-) concentration, and this I(-) concentration was approximately 30-fold higher than that measured in the serum. Also, expiratory effort, gross lung lesions, and pulmonary expression of an RSV antigen and IL-8 were reduced in the KI-treated lambs as compared with nontreated control lambs. Inhibition of LPO activity significantly increased lesions, RSV mRNA, and antigen. Similar experiments in 3-week-old lambs demonstrated that KI administration was associated with reduced gross lesions, decreased RSV titers in bronchoalveolar lavage fluid, and reduced RSV antigen expression. Overall, these data indicate that high-dose KI supplementation can be used in vivo to lessen the severity of RSV infections, potentially through the augmentation of mucosal oxidative defenses.

Sucrose stabilization of Respiratory Syncytial Virus (RSV) during nebulization and experimental infection

BACKGROUND

Respiratory syncytial virus (RSV) is a common respiratory pathogen that can cause severe pneumonia. In vivo studies of RSV can be difficult due to variation in viral infection and disease severity in some animal models. Factors that may contribute to the variation are decreases in viral titer due to preparation and storage and method of virus administration. Nebulization is one method of RSV administration that provides even distribution of virus to all lung lobes; however, the exact quantity of the virus killed by nebulization is not defined. To test the hypothesis that sucrose enhances RSV stability and infectivity, a series of in vitro experiments were conducted with RSV strain Memphis 37 stored at varying concentrations (0%, 3%, 5%, 8%, 10%, 15%, and 20%) of sucrose as a possible cryo- and nebulization protectant. The optimal in vitro concentration was then assessed in vivo in a lamb model.

METHODS

Prior to titering the virus on HEp-2 cells, the various virus solutions were subjected to one freeze-thaw cycle and one nebulization cycle. Forty-eight hours after viral plating, infectious foci were detected and counted using immunofluorescent imaging. Titers were determined after freeze-thaw and after freeze-thaw followed by nebulization, then compared to the stock titers (before freezing) as well as to one another to determine the loss of infectivity. To further test this in vivo, lambs 2 to 3-days-old were infected via nebulization with RSV using inoculate containing either 20% sucrose or no sucrose followed by assessments of infection severity.

RESULTS

Nebulization of virus in 0% sucrose resulted in a 0.580 log reduction in infectivity while virus in 20% sucrose exhibited a 0.297 log reduction. In vivo studies demonstrated that 20% sucrose enhanced RSV lesions and antigen distribution.

CONCLUSIONS

The data suggests that both nebulization and freeze-thawing of RSV in the absence of sucrose cause unacceptable losses in viral infectivity and that sucrose acts as a RSV protectant in both regards.

Lamb model of respiratory syncytial virus-associated lung disease: insights to pathogenesis and novel treatments

Preterm birth is a risk factor for respiratory syncytial virus (RSV) bronchiolitis and hospitalization. The pathogenesis underlying this is not fully understood, and in vivo studies are needed to better clarify essential cellular features and molecular mechanisms. Such studies include analysis of lung tissue from affected human infants and various animal models. The preterm and newborn lamb lung has developmental, structural, cellular, physiologic, and immunologic features similar to that of human infants. Also, the lamb lung is susceptible to various strains of RSV that infect infants and cause similar bronchiolar lesions. Studies in lambs suggest that viral replication in airways (especially bronchioles) is extensive by 4 days after infection, along with bronchiolitis characterized by degeneration and necrosis of epithelial cells, syncytial cell formation, neutrophil infiltration, epithelial cell hypertrophy and hyperplasia, and innate and adaptive immune responses. RSV bronchiolitis greatly affects airflow and gaseous exchange. RSV disease severity is increased in preterm lambs compared with full-term lambs; similar to human infants. The lamb is conducive to experimental assessment of novel, mechanistic therapeutic interventions such as delivery of vascular endothelial growth factor and enhancement of airway epithelial oxidative responses, Club (Clara) cell protein 10, and synthesized compounds such as nanobodies. In contrast, exposure of the fetal ovine lung in vivo to ethanol, a risk factor for preterm birth, reduces pulmonary alveolar development and surfactant protein A expression. Because the formalin-inactivated RSV vaccination enhances some inflammatory responses to RSV infection in lambs, this model has the potential to assess mechanisms of formalin-inactivated RSV enhanced disease as well as newly developed vaccines.

Effects of formalin-inactivated respiratory syncytial virus (FI-RSV) in the perinatal lamb model of RSV

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. There are currently no licensed vaccines or effective antivirals. The lack of a vaccine is partly due to increased caution following the aftermath of a failed clinical trial of a formalin-inactivated RSV vaccine (FI-RSV) conducted in the 1960’s that led to enhanced disease, necessitating hospitalization of 80% of vaccine recipients and resulting in two fatalities. Perinatal lamb lungs are similar in size, structure and physiology to those of human infants and are susceptible to human strains of RSV that induce similar lesions as those observed in infected human infants. We sought to determine if perinatal lambs immunized with FI-RSV would develop key features of vaccine-enhanced disease. This was tested in colostrum-deprived lambs immunized at 3–5 days of age with FI-RSV followed two weeks later by RSV infection. The FI-RSV-vaccinated lambs exhibited several key features of RSV vaccine-enhanced disease, including reduced RSV titers in bronchoalveolar lavage fluid and lung, and increased infiltration of peribronchiolar and perivascular lymphocytes compared to lambs either undergoing an acute RSV infection or naïve controls; all features of RSV vaccine-enhanced disease. These results represent a first step proof-of-principle demonstration that the lamb can develop altered responses to RSV following FI-RSV vaccination. The lamb model may be useful for future mechanistic studies as well as the assessment of RSV vaccines designed for infants.

Induction of interleukin-8 and interleukin-12 in neonatal ovine lung following experimental inoculation of bovine respiratory syncytial virus

This study aimed to determine the immunohistochemical expression of interleukin (IL)-1β, tumour necrosis factor alpha (TNF)-α, interferon (IFN)-γ, IL-4, IL-6, IL-8, IL-10 and IL-12 and to measure the concentrations of these cytokines in lung tissue from lambs infected experimentally with bovine respiratory syncytial virus (BRSV). Lambs (n = 15) were inoculated at 2 days of age with 20 ml of viral inoculum (1.26 × 10(6) TCID50 per ml) or sterile medium (n = 15). Rectal temperature, pulse and respiratory rates were monitored daily in control and infected lambs. Lambs were killed and subject to necropsy examination at 1, 3, 5, 7 and 15 days post inoculation (dpi). There was a temporal association between pulmonary expression of these cytokines and lung pathology in BRSV-infected lambs. The cytokines IL-4 and IL-10 were not elevated, but there was a significant increase in IL-1β, TNF-α, IFN-γ and IL-6 proteins and labelled cells, suggesting that these cytokines may play a role in the biological response to BRSV infection and contribute to the development of lung lesions. There was also a significant increase in the cytokine concentration and number of immunolabelled cells expressing IL-8 and IL-12 in infected lungs, suggesting that these cytokines might be used as therapeutic targets in the management of BRSV, in conjunction with measures to combat the causative pathogen and prophylactic methods aimed at preventing infection.

Chlorogenic acid inhibits the replication and viability of enterovirus 71 in vitro

Enterovirus 71 (EV71) is an etiology for a number of diseases in humans. Traditional Chinese herbs have been reported to be effective for treating EV71 infection. However, there is no report about the antiviral effects of CHA against EV71. In this study, plaque reduction assay demonstrated that the inhibitory concentration 50% (IC50) of CHA on EV71 replication is 6.3 µg/ml. When both CHA (20 µg/ml) and EV71 were added, or added post-infection at different time points, CHA was able to effectively inhibit EV71 replication between 0 and 10 h. In addition, CHA inhibited EV71 2A transcription and translation in EV71-infected RD cells, but did not affect VP1, 3C, and 3D expression. Furthermore, CHA inhibited secretions of IL-6, TNF-α, IFN-γ and MCP-1 in EV71-infected RD cells. Altogether, these results revealed that CHA may have antiviral properties for treating EV71 infection.

The Innate Immune System of the Perinatal Lung and Responses to Respiratory Syncytial Virus Infection

The response of the preterm and newborn lung to airborne pathogens, particles, and other insults is initially dependent on innate immune responses since adaptive responses may not fully mature and require weeks for sufficient responses to antigenic stimuli. Foreign material and microbial agents trigger soluble, cell surface, and cytoplasmic receptors that activate signaling cascades that invoke release of surfactant proteins, defensins, interferons, lactoferrin, oxidative products, and other innate immune substances that have antimicrobial activity, which can also influence adaptive responses. For viral infections such as respiratory syncytial virus (RSV), the pulmonary innate immune responses has an essential role in defense as there are no fully effective vaccines or therapies for RSV infections of humans and reinfections are common. Understanding the innate immune response by the preterm and newborn lung may lead to preventive strategies and more effective therapeutic regimens.

Perinatal lamb model of respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. Many animal models are used to study RSV, but most studies investigate disease in adult animals which does not address the unique physiology and immunology that makes infants more susceptible. The perinatal (preterm and term) lamb is a useful model of infant RSV disease as lambs have similar pulmonary structure including airway branching, Clara and type II cells, submucosal glands and Duox/lactoperoxidase (LPO) oxidative system, and prenatal alveologenesis. Lambs can be born preterm (90% gestation) and survive for experimentation although both preterm and term lambs are susceptible to ovine, bovine and human strains of RSV and develop clinical symptoms including fever, tachypnea, and malaise as well as mild to moderate gross and histologic lesions including bronchiolitis with epithelial injury, neutrophil infiltration and syncytial cell formation. RSV disease in preterm lambs is more severe than in term lambs; disease is progressively less in adults and age-dependent susceptibility is a feature similar to humans. Innate and adaptive immune responses by perinatal lambs closely parallel those of infants. The model is used to test therapeutic regimens, risk factors such as maternal ethanol consumption, and formalin inactivated RSV vaccines.