The pathogenesis of interstitial lung diseases in children.

The pathological changes observed in interstitial lung disease (ILD) are characterised by derangements of the alveolar walls. For a long time, the prevailing hypothesis has emphasised the key role of a persistent alveolitis that injures the lung and modulates fibrogenesis, regardless of initiating agents. The current concept on ILD pathogenesis relies on an epithelial/fibroblastic pathway with epithelial injury and activation, formation of subepithelial fibroblast/myofibroblast foci and excessive accumulation of extracellular matrix. An essential step in the restoration of alveolar integrity is the rapid re-epithelialisation of the altered surface, mainly through epithelial proliferation and migration. In the context of lung growth and development in paediatric ILD, it is suggested that the programmed production of mitogenic factors may promote the process of re-epithelialisation and may help to counteract the altered secretion of mediators involved in migration and proliferation of fibroblasts and differentiation into myofibroblasts. This is supported by clinical observations indicating that paediatric ILD is more responsive to therapeutic strategies than adult ILD.