The normal alveolar epithelial surface is covered predominantly by flat Type I pneumocytes, a cell which is very sensitive to injury, and to a lesser extent by cuboidal Type II cells. The Type II pneumocyte is usually a non-proliferative cell, but when the lung is injured, as in adult respiratory distress syndrome or idiopathic pulmonary fibrosis, the Type II cell proliferates and lines much of the alveolar surface. For a normal architecture to be restored, the hyperplastic Type II cells must differentiate into flat Type I cells. The control of Type II cell proliferation and differentiation is not well understood. The function and morphology of many epithelial cells are influenced by the basement membrane and extracellular matrix on which they rest. We propose to study show how extracellular matrix influences the proliferative response to Type II cells and their differentiation into Type I pneumocytes. Type II cells will be isolated from rats and identity confirmed by phospholipid composition, antisurfactant antibody binding, and the presence of lamaellar bodies on electron microscopy. The cells will be grown in culture on an acellular human amnion with intact basement membrane on one side and exposed interstitial stroma on the other. It is known that the morphology of Type II cells differs when grown on the two sides as assessed by light and scanning and transmission electron microscopy. We will assess proliferation of the cells on each side of the amnion by tritiated thymidine incorporation, counting of cell number and autoradiography. The differentiation of the cells will be probed by determination of their lectin binding profile. Function of the Type II cells will be assessed by their phospholipid and matrix secretion. In addition, studies of Type II cell morphology, proliferation, differentiation and function will be done during growth on a membrane previously damaged by activated polymorphonuclear leukocytes. Other factors, such as bronchoalveolar lavage (BAL) fluid, will be tested for stimulation of Type II cell proliferation in culture. BAL fluid from normal volunteers will be compared with that form patients with pulmonary diseases in which there is Type II cell hyperplasia. This approach should increase our understanding of the control of Type II cell proliferation and differentiation and of the role of the matrix in determining the repair of alveolar injury. New technologies used will include growth of alveolar Type II cells on an in vitro damaged matrix and detailed lectin binding analysis of Type I and II cells.
