Immunohistochemical evidence for the occurrence of similar epithelial phenotypes during lung development and radiation-induced fibrogenesis.

PURPOSE: Processes of fibrosis, wound healing and tissue regeneration have in common the fact that proliferation and differentiation of cells involved in the restoration of normal-tissue architecture resemble to a certain degree the embryonic development of the corresponding tissue. The present review focuses on the phenotypic changes of alveolar epithelial cells during fibrogenesis and describes similarities in the expression pattern of epithelial antigens during lung development.
METHODS: For comparative studies, immunohistochemical investigations of different experimental fibrosis models were performed.
RESULTS: For several epithelial proteins, such as the CD44 adhesion molecule, the enzymes carbanhydrase II and cathepsin D, as well as the lectin galectin-3, a transient epithelial immunoreactivity have been detected. What all four examples have in common is that a part of the foetal antigenic profile reappears under conditions of injury and during the development of pulmonary fibrosis.
CONCLUSIONS: The re-expression of foetal antigens in fibrotic samples with a spatio-temporal pattern, as detected by immunocytochemical techniques, indicates that some mechanisms or factors exist, which similarly regulate the differentiation of the epithelium during ontogenesis and in the remodelling process during fibrogenesis.