Enhanced viral replication and modulated innate immune responses in infant airway epithelium following H1N1 infection

Influenza: Toward understanding the immune response in the young

Annually influenza causes a global epidemic resulting in 290,000 to 650,000 deaths and extracts a massive toll on healthcare and the economy. Infants and children are more susceptible to infection and have more severe symptoms than adults likely mitigated by differences in their innate and adaptive immune responses. While it is unclear the exact mechanisms with which the young combat influenza, it is increasingly understood that their immune responses differ from adults. Specifically, underproduction of IFN-γ and IL-12 by the innate immune system likely hampers viral clearance while upregulation of IL-6 may create excessive damaging inflammation. The infant's adaptive immune system preferentially utilizes the Th-2 response that has been tied to γδ T cells and their production of IL-17, which may be less advantageous than the adult Th-1 response for antiviral immunity. This differential immune response of the young is considered to serve as a unique evolutionary adaptation such that they preferentially respond to infection broadly rather than a pathogen-specific one generated by adults. This unique function of the young immune system is temporally, and possibly mechanistically, tied to the microbiota, as they both develop in coordination early in life. Additional research into the relationship between the developing microbiota and the immune system is needed to develop therapies effective at combating influenza in the youngest and most vulnerable of our population.

Protective Intranasal Immunization Against Influenza Virus in Infant Mice Is Dependent on IL-6

Respiratory diseases adversely affect infants and are the focus of efforts to develop vaccinations and other modalities to prevent disease. The infant immune system differs from that of older children and adults in many ways that are as yet ill understood. We have used a C57BL/6 mouse model of infection with a laboratory- adapted strain of influenza (PR8) to delineate the importance of the cytokine IL-6 in the innate response to primary infection and in the development of protective immunity in adult mice. Herein, we used this same model in infant (14 days of age) mice to determine the effect of IL-6 deficiency. Infant wild type mice are more susceptible than older mice to infection, similar to the findings in humans. IL-6 is expressed in the lung in the early response to PR8 infection. While intramuscular immunization does not protect against lethal challenge, intranasal administration of heat inactivated virus is protective and correlates with expression of IL-6 in the lung, activation of lung CD8 cells, and development of an influenza-specific antibody response. In IL-6 deficient mice, this response is abrogated, and deficient mice are not protected against lethal challenge. These studies support the importance of the role of the tissue environment in infant immunity, and further suggest that IL-6 may be helpful in the generation of protective immune responses in infants.

Challenges for the Newborn Immune Response to Respiratory Virus Infection and Vaccination

The initial months of life reflect an extremely challenging time for newborns as a naïve immune system is bombarded with a large array of pathogens, commensals, and other foreign entities. In many instances, the immune response of young infants is dampened or altered, resulting in increased susceptibility and disease following infection. This is the result of both qualitative and quantitative changes in the response of multiple cell types across the immune system. Here we provide a review of the challenges associated with the newborn response to respiratory viral pathogens as well as the hurdles and advances for vaccine-mediated protection.

Effects of inhalation of sevoflurane at different concentrations on TRPV1 in airways of rats at different developmental stages

Aim Determine changes in the expressions of the ion channel-TRPV1-and neuropeptides-NKA, NKB, calcitonin gene-related peptide (CGRP), and SP-in 14-, 21-, and 42-day-old rats after inhaling 1.5% and 2.6% sevoflurane.

MAIN METHODS

A small in-house inhalation anesthesia chamber was designed to allow 14-, 21-, and 42-day-old rats inhale 1.5% and 2.6% sevoflurane, and rats in the control group inhaled carrier gas(1 L/min air +1 L/min O₂). In addition, 14- and 21-day-old rats were pretreated with capsazepine, followed by inhalation of 1.5% and 2.6% sevoflurane or the carrier gas. The expression of TRPV1 in lung tissues was detected by Western blotting, whereas the expressions of NKA, NKB, CGRP, and SP in the trachea were detected by immunohistochemistry.

KEY FINDINGS

After inhalation of 1.5% sevoflurane, the expression of TRPV1 in the lung tissues of 14- and 21-day-old rats was significantly increased compared with that in the control group, which was antagonized by capsazepine pretreatment. Moreover, inhalation of 1.5% sevoflurane markedly increased the expressions of NKA, NKB, CGRP, and SP in the trachea of 21-day-old rats and of NKB, CGRP, and SP in the trachea of 14-day-old rats. The expressions of these molecules were antagonized by capsazepine pretreatment. Conversely, inhalation of 2.6% sevoflurane decreased the expressions of NKA and NKB in the trachea of 42-day-old rats.

SIGNIFICANCE

Sevoflurane did not upregulate the expression of TRPV1 in the airways of late-developing rats. This anesthetic may have a two-way effect on airways, resulting in considerable effects in pediatric clinical anesthesia management.

Pulmonary surfactant lipids inhibit infections with the pandemic H1N1 influenza virus in several animal models

The influenza A (H1N1)pdm09 outbreak in 2009 exemplified the problems accompanying the emergence of novel influenza A virus (IAV) strains and their unanticipated virulence in populations with no pre-existing immunity. Neuraminidase inhibitors (NAIs) are currently the drugs of choice for intervention against IAV outbreaks, but there are concerns that NAI-resistant viruses can transmit to high-risk populations. These issues highlight the need for new approaches that address the annual influenza burden. In this study, we examined whether palmitoyl-oleoyl-phosphatidylglycerol (POPG) and phosphatidylinositol (PI) effectively antagonize (H1N1)pdm09 infection. POPG and PI markedly suppressed cytopathic effects and attenuated viral gene expression in (H1N1)pdm09-infected Madin-Darby canine kidney cells. POPG and PI bound to (H1N1)pdm09 with high affinity and disrupted viral spread from infected to noninfected cells in tissue culture and also reduced (H1N1)pdm09 propagation by a factor of 102 after viral infection was established in vitro In a mouse infection model of (H1N1)pdm09, POPG and PI significantly reduced lung inflammation and viral burden. Of note, when mice were challenged with a typically lethal dose of 1000 plaque-forming units of (H1N1)pdm09, survival after 10 days was 100% (14 of 14 mice) with the POPG treatment compared with 0% (0 of 14 mice) without this treatment. POPG also significantly reduced inflammatory infiltrates and the viral burden induced by (H1N1)pdm09 infection in a ferret model. These findings indicate that anionic phospholipids potently and efficiently disrupt influenza infections in animal models.

Nonhuman Primate Models of Respiratory Disease: Past, Present, and Future

The respiratory system consists of an integrated network of organs and structures that primarily function for gas exchange. In mammals, oxygen and carbon dioxide are transmitted through a complex respiratory tract, consisting of the nasal passages, pharynx, larynx, and lung. Exposure to ambient air throughout the lifespan imposes vulnerability of the respiratory system to environmental challenges that can contribute toward development of disease. The importance of the respiratory system to human health is supported by statistics from the Centers for Disease Control and Prevention; in 2015, chronic lower respiratory diseases were the third leading cause of death in the United States. In light of the significant mortality associated with respiratory conditions that afflict all ages of the human population, this review will focus on basic and preclinical research conducted in nonhuman primate models of respiratory disease. In comparison with other laboratory animals, the nonhuman primate lung most closely resembles the human lung in structure, physiology, and mucosal immune mechanisms. Studies defining the influence of inhaled microbes, pollutants, or allergens on the nonhuman primate lung have provided insight on disease pathogenesis, with the potential for elucidation of molecular targets leading to new treatment modalities. Vaccine trials in nonhuman primates have been crucial for confirmation of safety and protective efficacy against infectious diseases of the lung in a laboratory animal model that recapitulates pathology observed in humans. In looking to the future, nonhuman primate models of respiratory diseases will continue to be instrumental for translating biomedical research for improvement of human health.

Comparative Transcriptomic and Metagenomic Analyses of Influenza Virus-Infected Nasal Epithelial Cells From Multiple Individuals Reveal Specific Nasal-Initiated Signatures

In vitro and in vivo research based on cell lines and animals are likely to be insufficient in elucidating authentic biological and physiological phenomena mimicking human systems, especially for generating pre-clinical data on targets and biomarkers. There is an obvious need for a model that can further bridge the gap in translating pre-clinical findings into clinical applications. We have previously generated a model of in vitro differentiated human nasal epithelial cells (hNECs) which elucidated the nasal-initiated repertoire of immune responses against respiratory viruses such as influenza A virus and rhinovirus. To assess their clinical utility, we performed a microarray analysis of influenza virus-infected hNECs to elucidate nasal epithelial-initiated responses. This was followed by a metagenomic analysis which revealed transcriptomic changes comparable with clinical influenza datasets. The primary target of influenza infection was observed to be the initiator of innate and adaptive immune genes, leaning toward type-1 inflammatory activation. In addition, the model also elucidated a down-regulation of metabolic processes specific to the nasal epithelium, and not present in other models. Furthermore, the hNEC model detected all 11 gene signatures unique to influenza infection identified from a previous study, thus supporting the utility of nasal-based diagnosis in clinical settings. In conclusion, this study highlights that hNECs can serve as a model for nasal-based clinical translational studies and diagnosis to unravel nasal epithelial responses to influenza in the population, and as a means to identify novel molecular diagnostic markers of severity.

Innate Immunity to Respiratory Infection in Early Life

Early life is a period of particular susceptibility to respiratory infections and symptoms are frequently more severe in infants than in adults. The neonatal immune system is generally held to be deficient in most compartments; responses to innate stimuli are weak, antigen-presenting cells have poor immunostimulatory activity and adaptive lymphocyte responses are limited, leading to poor immune memory and ineffective vaccine responses. For mucosal surfaces such as the lung, which is continuously exposed to airborne antigen and to potential pathogenic invasion, the ability to discriminate between harmless and potentially dangerous antigens is essential, to prevent inflammation that could lead to loss of gaseous exchange and damage to the developing lung tissue. We have only recently begun to define the differences in respiratory immunity in early life and its environmental and developmental influences. The innate immune system may be of relatively greater importance than the adaptive immune system in the neonatal and infant period than later in life, as it does not require specific antigenic experience. A better understanding of what constitutes protective innate immunity in the respiratory tract in this age group and the factors that influence its development should allow us to predict why certain infants are vulnerable to severe respiratory infections, design treatments to accelerate the development of protective immunity, and design age specific adjuvants to better boost immunity to infection in the lung.

The Helicobacter pylori type IV secretion system promotes IL-8 synthesis in a model of pediatric airway epithelium via p38 MAP kinase

Epidemiologic studies have reported an inverse relationship between childhood Helicobacter pylori infection and development of allergic asthma. Because lung epithelium plays an important role in allergic asthma pathogenesis, we hypothesized that H. pylori may directly influence airway epithelial cell innate immune function, particularly in early childhood. To test our hypothesis, we established an in vitro H. pylori infection model using primary tracheobronchial epithelial cell cultures derived from infant, juvenile and adult rhesus monkeys. Airway epithelial cell cultures were infected with wild-type or cag pathogenicity island mutant H. pylori strains, followed by evaluation of IL-8 and IL-6 protein synthesis. We found that H. pylori primarily increased IL-8 synthesis in a MOI and age-dependent fashion, with a greater than 4-fold induction in infant versus adult cultures. H. pylori-induced IL-8 synthesis in infant and juvenile cultures was significantly reduced by cag pathogenicity island mutants, indicating a requirement for the type IV secretion system. Although peptidoglycan recognition of nucleotide binding oligomerization domain-containing protein 1 (NOD1) and NF-kappaB have been implicated as key cytokine signaling molecules for H. pylori infection in gastric epithelium, NOD1 (ML130) or NF-kappaB (JSH-23) inhibitors minimally affected IL-8 synthesis in airway epithelial cell cultures following H. pylori infection. In contrast, inhibition of the p38 MAP kinase pathway (SB203580) resulted in almost complete suppression of H. pylori-induced IL-8 synthesis. Collectively, these results indicate that H. pylori can preferentially elicit IL-8 synthesis in a model of pediatric airway epithelium using the type IV secretion system via p38 MAP kinase.

Attenuated Airway Epithelial Cell Interleukin-22R1 Expression in the Infant Nonhuman Primate Lung

Respiratory tract infections are a leading cause of morbidity and mortality in children under 5 years of age. Increased susceptibility to infection is associated with deficiencies in immunity during early childhood. Airway epithelium represents the first line of mucosal defense against inhaled pathogens. However, little is known about epithelial immune mechanisms in the maturing lung. IL-22 and its receptor IL-22R1 are important in host defense and repair of epithelial barriers. The objective of this study was to determine whether a quantitative difference in IL-22R1 exists between infant and adult airways using the rhesus macaque monkey as a model of childhood lung development. Immunofluorescence staining of tracheal tissue revealed minimal expression of IL-22R1 in epithelium at 1 month of age, with a progressive increase in fluorescence-positive basal cells through 1 year of age. Western blot analysis of tracheal lysates confirmed significant age-dependent differences in IL-22R1 protein content. Further, primary tracheobronchial epithelial cell cultures established from infant and adult monkeys showed differential IL-22R1 mRNA and protein expression in vitro. To begin to assess the regulation of age-dependent IL-22R1 expression in airway epithelium, the effect of histone deacetylase and DNA methyltransferase inhibitors was evaluated. IL-22R1 mRNA in adult cultures was not altered by 5-aza-2'-deoxycytidine or trichostatin A. IL-22R1 mRNA in infant cultures showed no change with 5-aza-2'-deoxycytidine but was significantly increased after trichostatin A treatment; however, IL-22R1 protein did not increase concurrently. These data suggest that IL-22R1 in airway epithelium is regulated, in part, by epigenetic mechanisms that are dependent on chronologic age.

Influenza A Virus Infection, Innate Immunity, and Childhood

Infection with influenza A virus is responsible for considerable morbidity and mortality in children worldwide. While it is apparent that adequate activation of the innate immune system is essential for pathogen clearance and host survival, an excessive inflammatory response to infection is detrimental to the young host. A review of the literature indicates that innate immune responses change throughout childhood. Whether these changes are genetically programmed or triggered by environmental cues is unknown. The objectives of this review are to summarize the role of innate immunity in influenza A virus infection in the young child and to highlight possible differences between children and adults that may make children more susceptible to severe influenza A infection. A better understanding of age-related differences in innate immune signaling will be essential to improve care for this high-risk population.

The use of nonhuman primates in research on seasonal, pandemic and avian influenza, 1893-2014

Attempts to reproduce the features of human influenza in laboratory animals date from the early 1890s, when Richard Pfeiffer inoculated apes with bacteria recovered from influenza patients and produced a mild respiratory illness. Numerous studies employing nonhuman primates (NHPs) were performed during the 1918 pandemic and the following decade. Most used bacterial preparations to infect animals, but some sought a filterable agent for the disease. Since the viral etiology of influenza was established in the early 1930s, studies in NHPs have been supplemented by a much larger number of experiments in mice, ferrets and human volunteers. However, the emergence of a novel swine-origin H1N1 influenza virus in 1976 and the highly pathogenic H5N1 avian influenza virus in 1997 stimulated an increase in NHP research, because these agents are difficult to study in naturally infected patients and cannot be administered to human volunteers. In this paper, we review the published literature on the use of NHPs in influenza research from 1893 through the end of 2014. The first section summarizes observational studies of naturally occurring influenza-like syndromes in wild and captive primates, including serologic investigations. The second provides a chronological account of experimental infections of NHPs, beginning with Pfeiffer's study and covering all published research on seasonal and pandemic influenza viruses, including vaccine and antiviral drug testing. The third section reviews experimental infections of NHPs with avian influenza viruses that have caused disease in humans since 1997. The paper concludes with suggestions for further studies to more clearly define and optimize the role of NHPs as experimental animals for influenza research.