Morphological and molecular markers in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a progressive, lethal, interstitial lung disease with no proven effective therapy other than lung transplantation. A definitive diagnosis of the disease requires surgical lung biopsy to show a histological appearance of usual interstitial pneumonia. The main histological features include temporal and spatial heterogeneity, fibroblastic foci, extracellular matrix deposition with vessel remodeling and honeycomb changes. There are some morphological aspects that have recently been taken into account as possible prognostic markers for disease progression. Although the cellular and molecular pathways driving disease pathogenesis are complex and not fully delineated, increasing evidence suggests that a key event is ongoing alveolar epithelial injury in association with an abnormal host repair response. Inflammation seems to play a less important role and remains largely debated while increased attention has been on the role of noninflammatory structural cells, such as fibroblasts, epithelial cells and endothelial cells. The modifications and interactions among these cells are complex and regulated by various molecular factors. This article reviews the morphology of the disease, focusing on some new facets and on the principal molecular factors involved in the different aspects of parenchymal remodeling.