Differential Expression of Laminins and Their Integrin Receptors in Developing and Adult Human Lung

Here, the authors studied the expression of different laminin chains and their integrin receptors in fetal and adult lung by immunohistochemistry. Special attention was focused on the changes in the expression of these proteins during the development from the pseudoglandular (PG) and canalicular stages to adult lung and on the possible implications of the changes for the normal lung development. The most significant changes in the expression pattern were found during the development from the PO stage to the canalicular stage. Basement membranes (BM) of both the epithelial buds and the becoming bronchi showed reactivity for laminin α1, a3, and B3 chains at all stages. The a2 chain was expressed only in the epithelial buds at the PO stage, and could not be found in any epithelial structures at the canalicular stage. Similarly, at the PG stage the B2 chain was expressed in BMs of both epithelial buds and bronchi but disappeared from the bronchial BM before the canalicular stage. The B1 chain appeared in the bronchial BM first in the mature lung. There were considerable changes in the expression of integrins (lnt) comcomitantly with alterations in the composition of the BMs. At the PG stage, the epithelial buds showed reactivity for integrin a2, a3, and a6 subunits, but at the canalicular stage the integrin a2 and a6 subunits disappeared, and only the a3 integrin subunit was found in evolving alveolar walls; integrin a6 was found in capillaries.  Our results suggest that there are major changes in the expression of laminin and their integrin receptors during morphogenesis of the lung, which may be important for normal development.