Lung development and emerging roles for type 2 immunity.
Lung development is a complex process mediated through the interaction of multiple cell types, factors and mediators. In mice, it starts as early as embryonic day 9 and continues into early adulthood. The process can be separated into five different developmental stages: embryonic, pseudoglandular, canalicular, saccular and alveolar. Whilst lung bud formation and branching morphogenesis have been studied extensively, the mechanisms of alveolarization are incompletely understood. Aberrant lung development can lead to deleterious consequences for respiratory health such as bronchopulmonary dysplasia, a disease primarily affecting preterm neonates, which is characterized by increased pulmonary inflammation and disturbed alveolarization. While the deleterious effects of type 1-mediated inflammatory responses on lung development have been well established, the role of type 2 responses in postnatal lung development remains poorly understood. Recent studies indicate that type 2-associated immune cells, such as group 2 innate lymphoid cells and alveolar macrophages, are increased in number during postnatal alveolarization. Here, we present the current state of understanding of the postnatal stages of lung development and the key cell types and mediators known to be involved. We also provide an overview of how stem cells are involved in lung development and regeneration, and the negative influences of respiratory infections. This article is protected by copyright. All rights reserved.
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