Unlabelled

Influenza is the cause of significant morbidity and mortality in pediatric populations. The contribution of pulmonary host defense mechanisms to viral respiratory infection susceptibility in very young children is poorly understood. As a surrogate to compare mucosal immune responses of infant and adult lungs, rhesus monkey primary airway epithelial cell cultures were infected with pandemic influenza A/H1N1 virus in vitro. Virus replication, cytokine secretion, cell viability, and type I interferon (IFN) pathway PCR array profiles were evaluated for both infant and adult cultures. In comparison with adult cultures, infant cultures showed significantly increased levels of H1N1 replication, reduced alpha interferon (IFN-α) protein synthesis, and no difference in cell death following infection. Age-dependent differences in expression levels of multiple genes associated with the type I IFN pathway were observed in H1N1-infected cultures. To investigate the pulmonary and systemic responses to H1N1 infection in early life, infant monkeys were inoculated with H1N1 by upper airway administration. Animals were monitored for virus and parameters of inflammation over a 14-day period. High H1N1 titers were recovered from airways at day 1, with viral RNA remaining detectable until day 9 postinfection. Despite viral clearance, bronchiolitis and alveolitis persisted at day 14 postinfection; histopathological analysis revealed alveolar septal thickening and intermittent type II pneumocyte hyperplasia. Our overall findings are consistent with the known susceptibility of pediatric populations to respiratory virus infection and suggest that intrinsic developmental differences in airway epithelial cell immune function may contribute to the limited efficacy of host defense during early childhood.

Importance

To the best of our knowledge, this study represents the first report of intrinsic developmental differences in infant airway epithelial cells that may contribute to the increased susceptibility of the host to respiratory virus infections. Despite the global burden of influenza, there are currently no vaccine formulations approved for children <6 months of age. Given the challenges of conducting experimental studies involving pediatric patients, rhesus monkeys are an ideal laboratory animal model to investigate the maturation of pulmonary mucosal immune mechanisms during early life because they are most similar to those of humans with regard to postnatal maturation of the lung structure and the immune system. Thus, our findings are highly relevant to translational medicine, and these data may ultimately lead to novel approaches that enhance airway immunity in very young children.

Exposure to household air pollution (HAP) from solid fuel combustion affects almost half of the world population. Adverse respiratory outcomes such as respiratory infections, impaired lung growth and chronic obstructive pulmonary disease have been linked to HAP exposure. Solid fuel smoke is a heterogeneous mixture of various gases and particulates. Cell culture and animal studies with controlled exposure conditions and genetic homogeneity provide important insights into HAP mechanisms. Impaired bacterial phagocytosis in exposed human alveolar macrophages possibly mediates several HAP-related health effects. Lung pathological findings in HAP-exposed individuals demonstrate greater small airways fibrosis and less emphysema compared with cigarette smokers. Field studies using questionnaires, air pollution monitoring and/or biomarkers are needed to better establish human risks. Some, but not all, studies suggest that improving cookstove efficiency or venting emissions may be associated with reduced respiratory symptoms, lung function decline in women and severe pneumonia in children. Current studies focus on fuel switching, stove technology replacements or upgrades and air filter devices. Several governments have initiated major programmes to accelerate the upgrade from solid fuels to clean fuels, particularly liquid petroleum gas, which provides research opportunities for the respiratory health community.