Structural and functional relationships between type II pneumocytes and components of extracellular matrices.

Type II pneumocytes of the pulmonary alveolus are dynamic cells with multiple functional capabilities in vivo, including secretion of surface-active lipoproteins and cell renewal of the epithelial lining of the alveolus, involving its differentiation into another cell type (the type I pneumocyte). The factors that influence and control these processes, which are vital to the function of the alveolus, have begun to be more clearly understood in recent years, in large part because of the development of adequate in vitro systems, which permit the manipulation of relevant variables. These appear to be a complex interaction between insoluble components of extracellular matrices, principally of the basement membrane, and soluble factors that include hormones and growth factors. This review focuses particularly on those components of extracellular matrices that specifically and nonspecifically impact on type II cell function, and it attempts to bring together the diverse technical approaches used to define and examine these relationships cytochemically and functionally.