Type IV collagen alpha chains of the basement membrane in the rat bronchioalveolar transitional segment

In the present study, we have analyzed the α(IV) chain distribution in the subepithelial basement membrane (BM) of the rat pulmonary airway from the bronchi to alveoli. We have furthermore analyzed the α(IV) chain distribution in the subepithelial BM of the bronchioalveolar duct junction (BADJ) using α(IV) chain specific monoclonal antibodies. Our results show that the BM of the bronchial and bronchiolar epithelium contains [α1(IV)]2 α2(IV) and [α5(IV)]2 α6(IV) molecules and confirmed that the alveolar BM consists of [ α1(IV)]2 α2(IV) and α3(IV) α4(IV) α5(IV) molecules. There are also small regions in BADJ consisting of only [ α1(IV)]2 α2(IV) molecules without α3(IV) α4(IV) α5(IV) and [ α5(IV)]2 α6(IV) molecules. Moreover, the bronchioalveolar stem cells (BASCs) - primordial cells for bronchiolar Clara cells and alveolar type II (AT2) cells - lie adjacent to such small regions. These findings suggest that [α1(IV)]2 α2(IV) may be important for the BASCs to self-renew or to self-maintain themselves and that microenvironments produced by α(IV) chains may be important for cell differentiation.